Short answer
- World War I started in 1914. The standard start date used by reference works such as Encyclopaedia Britannica is July 28, 1914, the day Austria-Hungary declared war on Serbia. That declaration did not come out of nowhere. It followed the assassination of Archduke Franz Ferdinand and his wife Sophie in Sarajevo on June 28, 1914, and a month of failed diplomacy known as the July Crisis. Within about a week of the July 28 declaration, Germany, Russia, France, and Britain were also at war, and a Balkan conflict had become a European war. It would later become a world war as empires, colonies, and additional states were drawn in. If you need only one year for an exam answer, a quiz, or a timeline, write 1914. The rest of this article explains why historians choose that year, why June 28 is not the start date, and why dates such as 1917, 1918, and 1919 sometimes appear in answers that confuse the start of the war with American entry, the armistice, or the peace treaty.
The One Year Answer: 1914
Encyclopaedia Britannica dates World War I from July 28, 1914 to November 11, 1918. That range is the most useful single answer to the question in the title, because it marks the war from its first declaration of war between two states to the armistice that stopped the fighting on the Western Front. The war is also known as the First World War, the Great War, and WWI. During the war itself, many people called it the Great War. The name First World War became the common distinguishing name only after a second world war made the numbering necessary.
The year 1914 also matters because it separates causes from outbreak. The deeper causes of the war, such as rival alliances, nationalism, imperial competition, and military buildups, had been developing for years. None of those causes, on its own, gives a start year. A war starts when states decide to fight, declare war, or open hostilities. In 1914, those decisions happened in a concentrated sequence across five weeks in the summer. That concentration is why 1914, rather than an earlier year of rising tension, is the answer.
It is worth stating plainly what 1914 does not mean. It does not mean that every country entered the war in 1914. Italy was neutral in 1914 and joined the Allied side in 1915, the Ottoman Empire joined the Central Powers in October 1914, and the United States did not enter until 1917. A start year describes when the war began, not when each participant joined it. That distinction explains many wrong answers given by people who remember the year their own country entered rather than the year the war itself began.
Why July 28, 1914 Is the Standard Start Date
Historians need a convention for dating a war that grew step by step rather than starting everywhere at once. The convention used by Britannica and by the United States Holocaust Memorial Museum is to date the start to the first declaration of war in the chain: Austria-Hungary’s declaration of war on Serbia on July 28, 1914. That choice has three strengths. First, it is a clear, documented state act, not a vague turning point. Second, it marks the moment when diplomacy gave way to a declared war between two states. Third, it sits at the start of the chain reaction that followed.
Other dates in the same summer mark different stages of the same outbreak, and they are useful precisely because they show how fast the crisis moved. Germany declared war on Russia on August 1, 1914, and on France on August 3, 1914. Britain declared war on Germany on August 4, 1914, after Germany invaded neutral Belgium. By early August, most of the major European powers were at war. If someone says the war started in early August 1914, they are describing the moment the war became general in Europe. That is not wrong as a description, but it is not the standard start date, because the declared war between Austria-Hungary and Serbia already existed by then.
There is also a difference between a declaration of war and the first shots. Some accounts focus on first fighting rather than first declaration, which can shift the emphasis by days. For the question “what year did World War I start,” that difference does not change the year. Whether you count from the declaration on July 28 or from the fighting that followed, the year is still 1914.
Sarajevo: June 28, 1914, the Spark, Not the Start
On June 28, 1914, Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, and his wife Sophie, Duchess of Hohenberg, were assassinated in Sarajevo by Gavrilo Princip, a Bosnian Serb nationalist. The assassination is often called the spark that set off the war, and that metaphor is useful if it is not taken too literally. A spark needs flammable material around it, and Europe in 1914 supplied that material in the form of alliances, rivalries, and military plans. The assassination did not create those conditions. It set off a crisis inside them.
It is important not to confuse the spark with the start. June 28 was an assassination, not a declaration of war, and no state was at war on that day as a result of the shooting alone. A full month passed between the assassination and the declaration of war on Serbia. During that month, leaders exchanged messages, sought assurances from allies, prepared military plans, and debated whether a local war could be kept local. The war was not an automatic reflex in the hour after Sarajevo. It was the outcome of decisions made across July, which is why the crisis as a whole is called the July Crisis.
The assassination also needs to be described without turning one young man into the sole cause of a world war. Princip was part of a group of conspirators, and Austria-Hungary suspected Serbian backing for the plot. Historians still debate how much the Serbian government knew. What is not debated is the basic sequence: the assassination on June 28, 1914, was the immediate trigger for the July Crisis, and the July Crisis led to the declaration of war on July 28, 1914. Keeping the trigger and the declaration separate is the key to answering the start year question correctly.
The July Crisis, Step by Step
The July Crisis is the name for the diplomatic and military escalation between the assassination on June 28, 1914, and the general European war of early August 1914. The steps below follow the sequence recorded by the United States Holocaust Memorial Museum and Imperial War Museums. They show how a crisis between two states became a continental war, and then a world war.
First, Austria-Hungary, supported by Germany, issued an ultimatum to Serbia on July 23, 1914. The ultimatum demanded, among other things, that Serbia stop activities directed against Austria-Hungary and accept Austrian involvement in investigating the assassination. Serbia’s reply accepted many points but did not satisfy Vienna, particularly on the question of Austrian officials operating inside Serbia. Austria-Hungary treated the reply as inadequate and broke off diplomatic relations.
Second, Austria-Hungary declared war on Serbia on July 28, 1914. This is the standard start date for the war. At this point, the conflict was still, in formal terms, a war between Austria-Hungary and Serbia. Within days, it stopped being only that war, because both states had allies and protectors with their own commitments and fears.
Third, Russia entered the conflict on Serbia’s side. Russia saw itself as a protector of Serbia and of Slavic peoples in the Balkans, and it also feared that a crushing Austrian victory over Serbia would weaken Russian influence in the region. Russian mobilization, the calling up and movement of armed forces for war, alarmed Germany, which faced the prospect of war with Russia in the east while also facing France in the west.
Fourth, Germany declared war on Russia on August 1, 1914, and on France on August 3, 1914. Germany’s war plan aimed to defeat France quickly before turning fully to Russia, and that plan required moving through Belgium. The invasion of neutral Belgium then brought Britain into the war. Britain declared war on Germany on August 4, 1914, citing both the violation of Belgian neutrality, which Britain had guaranteed under the Treaty of London of 1839, and the fear of German domination of Europe.
Fifth, the war widened beyond Europe. Britain’s declaration bound its empire, so Canada, Australia, New Zealand, India, South Africa, and other parts of the empire were drawn into the war effort. Colonial forces fought in Africa, the Middle East, and elsewhere, and the Ottoman Empire’s entry in October 1914 opened additional fronts. By the end of 1914, the war involved fighting on multiple continents and oceans, which is why the name world war fits, even though the heaviest fighting in memory remains the Western Front in France and Belgium.
The table below summarizes the core outbreak sequence. The point is the order and the speed, not every declaration by every smaller state.
| Date in 1914 | Event |
|---|---|
| June 28 | Archduke Franz Ferdinand and Sophie assassinated in Sarajevo |
| July 23 | Austria-Hungary issues an ultimatum to Serbia |
| July 28 | Austria-Hungary declares war on Serbia: the standard start date |
| August 1 | Germany declares war on Russia |
| August 3 | Germany declares war on France |
| August 4 | Britain declares war on Germany after the invasion of Belgium |
The Deeper Causes: Why a Local Crisis Became a World War
The July Crisis explains when the war started. It does not fully explain why a Balkan assassination led to a world war. For that, historians point to longer term conditions that made European leaders more willing to risk war and less able to contain it. These causes are contested in their relative weight, and this article presents them as contributing conditions, not as a single agreed ranking.
The alliance system is the most direct link between a local war and a general war. By 1907, Europe was divided into two main camps: the Triple Alliance of Germany, Austria-Hungary, and Italy, and the Triple Entente of France, Russia, and Britain. Alliances were meant to deter attack by promising support, but in a crisis they also created chains of obligation. A war between Austria-Hungary and Serbia pulled in Russia, which pulled in Germany, which pulled in France, which, through Belgium, pulled in Britain. Italy is the exception that proves the complexity: Italy was a member of the Triple Alliance but declared neutrality in 1914 and later joined the Allied side in 1915. Alliances shaped the war, but they did not operate as automatic switches.
Nationalism was a second condition. In the Balkans, Serbian nationalism sought to unite South Slav peoples, which threatened the multiethnic Austro-Hungarian Empire. In western Europe, French nationalism sought the return of Alsace-Lorraine, territory lost to Germany in the Franco-Prussian War of 1870 to 1871. Nationalism made compromise look like weakness in each capital, and it made leaders fear that backing down would cost them support at home.
Imperial rivalry was a third condition. Britain, France, Germany, and other powers competed for colonies, markets, and naval power. Disputes over Morocco and other colonial questions had already brought Europe close to crisis before 1914. Imperial competition did not cause the Sarajevo assassination, but it deepened distrust, so each crisis was read as part of a larger struggle for power.
Militarism and military planning were a fourth condition. European states had built large armies and navies, and their war plans emphasized speed. Mobilization timetables were rigid: once one state mobilized, its rivals felt they had to mobilize too, or risk being caught unprepared. That logic turned diplomatic delays into military dangers.
Historians disagree about how to weigh these causes, and about how much blame should fall on any one government. Some interpretations stress German decisions in July 1914, including Germany’s assurance of support to Austria-Hungary, often called the blank check. Others stress a shared failure of diplomacy, in which several governments misjudged their rivals or believed a short war was possible. Still others stress structural forces, such as the alliance system and mobilization plans, that limited the choices of individual leaders. This article does not settle that debate, because the start year question does not require settling it. Whatever weight is given to each cause, the war that resulted began in 1914, and the debate is about responsibility for that outbreak, not about the year.
What Germany Did, and What This Article Does Not Duplicate
Readers sometimes look for a Germany centered account of the war, and that is a different question from the start year question. Germany’s role in July 1914 included supporting Austria-Hungary, declaring war on Russia and France in early August, and invading Belgium, which brought Britain into the war. Those actions are summarized here only as part of the outbreak sequence, because they are necessary to explain how the war became general.
A fuller account of Germany’s aims, its war planning, its conduct of the war, and the later debate about German responsibility belongs in a companion article on Germany in the First World War, identified as AMB-526. Readers who want that fuller treatment should read that article next, rather than expecting this article to repeat it. Keeping the two articles separate follows the one intent per page principle: this article answers when the war started, and the companion article covers Germany’s role in it.
How the War Ended, So the End Dates Do Not Confuse the Start Date
The end of the war is a common source of confusion, because the war has more than one end date, just as it has more than one outbreak date. The fighting on the Western Front stopped with the armistice of November 11, 1918. The armistice was signed in the morning and took effect at 11 a.m., which is why November 11 is remembered as Armistice Day or Remembrance Day in many countries. Britannica therefore ends its date range for the war on November 11, 1918.
The armistice was not a peace treaty. It was an agreement to stop fighting while a peace settlement was negotiated. The Treaty of Versailles, the main peace treaty with Germany, was signed on June 28, 1919, exactly five years after the Sarajevo assassination. Other treaties with the other Central Powers followed, and the United States made a separate peace with Germany in 1921 after the Senate rejected the Treaty of Versailles. None of those later dates changes the start year. A war that began in 1914 can end in stages in 1918 and 1919, and both facts can be true at the same time.
The human cost also belongs in any honest account of the war, even a short explainer about its start date. Britannica states that as many as 8.5 million soldiers and 13 million civilians died as a result of the war. Those are upper range estimates, not exact counts, and other sources give different totals depending on what they count, including deaths from disease, famine, and the influenza pandemic of 1918 and 1919. The point is that a war that began with a single assassination in Sarajevo grew into a conflict whose death toll ran into the millions, which is why the question of how it started still matters.
Why Other Years Are Sometimes Cited
If the answer is so clearly 1914, why do other years appear in conversation, in quizzes, and in search results? The table below lists the most common confusions and the correct place of each year in the story.
| Year sometimes cited | What actually happened | Why it is not the start year |
|---|---|---|
| 1912 or 1913 | The Balkan Wars of 1912 to 1913 reshaped the Balkans and raised tensions between Serbia, Austria-Hungary, and other powers | These wars were earlier Balkan conflicts, not World War I itself, although they form part of its background |
| 1915 | Italy joined the Allied side, and the Second Battle of Ypres took place | By 1915 the war was already well under way; Italy’s entry widened it but did not start it |
| 1917 | The United States entered the war on April 6, 1917, and Russia went through two revolutions that year before leaving the war in 1918 | 1917 marks American entry and Russian upheaval, not the outbreak of the war |
| 1918 | The armistice of November 11, 1918 stopped the fighting on the Western Front | 1918 is the year the fighting stopped, not the year it started |
| 1919 | The Treaty of Versailles was signed on June 28, 1919 | 1919 is the year of the main peace treaty with Germany, not the year the war began |
Two other confusions deserve a direct answer. First, some people date the war to 1914 but give the month as June, because they remember the assassination. June 28, 1914, is the trigger date, and July 28, 1914, is the declaration date. Both are in 1914, so the year answer is safe either way, but only July 28 is the standard start date. Second, some people say the war started in August 1914, because that is when Britain, France, and Germany were all at war. August 1914 describes the general European war, and it is a useful shorthand for a British or French centered account. It does not replace July 28 as the first declaration in the chain.
Finally, people sometimes ask whether World War I and the Great War are two different wars. They are not. They are two names for the same war of 1914 to 1918. World War II is the later war of 1939 to 1945, and it is a separate conflict, even though its origins are connected to the settlement that ended the First World War.
How Historians Date a War That Grew Step by Step
There is no single physical moment at which a world war switches on. Historians therefore use conventions, and it helps to know what convention is being used when you read a date. The most common convention, used by Britannica, is the first declaration of war in the chain that became the general war. A second convention is the first major fighting between the main powers, which for 1914 would point to early August. A third convention is the date a particular country entered, which is why American textbooks sometimes emphasize 1917 and British accounts sometimes emphasize August 4, 1914. They answer slightly different questions: when did the war begin, when did it become general, and when did our country join it.
For a general reference answer, the first convention is the best choice, because it is the most consistent across countries. It does not privilege the entry date of any one state. It also matches timelines that list July 28, 1914 to November 11, 1918. If an exam or textbook uses a different convention, it will usually say so, for example by asking when Britain entered the war or when the United States entered the war. Those are narrower questions, with narrower answers: Britain on August 4, 1914, and the United States on April 6, 1917.
The same logic applies to the end of the war. The armistice of November 11, 1918, is the standard end date for the fighting, while the Treaty of Versailles of June 28, 1919, is the standard date for the formal peace with Germany. A careful answer to the start question does the same: 1914, with July 28, 1914, as the standard start date, June 28, 1914, as the trigger, and early August 1914 as the moment the war became general in Europe.
Common Mistakes to Avoid
The most common mistake is to give the assassination date as the start date. June 28, 1914, is the date Franz Ferdinand was killed. July 28, 1914, is the date Austria-Hungary declared war on Serbia. The two dates are exactly one month apart, which makes the confusion easy and also easy to fix once the pair is memorized together: June for the assassination, July for the declaration.
The second most common mistake is to give the year a country entered the war as the year the war started. The United States entered in 1917. Italy entered in 1915. The Ottoman Empire entered in 1914 but in October, months after the standard start date. Each of those years is correct for its own question and wrong for the general question.
The third mistake is to treat the Treaty of Versailles as the end of the war in the same sense as the armistice. The armistice stopped the fighting in 1918. The treaty set the peace terms in 1919. The war started with declarations, not with a treaty.
The fourth mistake is to assign the whole war to a single cause or a single villain. The assassination was the trigger, but the war required alliances, rivalries, military plans, and a series of government decisions in July 1914. A balanced account names the trigger, describes the crisis, and acknowledges the debate about responsibility.
Frequently Asked Questions
What year did World War I start?
World War I started in 1914. The standard start date is July 28, 1914, when Austria-Hungary declared war on Serbia.
What happened on June 28, 1914?
Archduke Franz Ferdinand and his wife Sophie were assassinated in Sarajevo on June 28, 1914. That assassination triggered the July Crisis, which led to the declaration of war a month later. June 28 is the trigger date, not the start date of the war itself.
Why is July 28, 1914, used as the start date instead of August 4, 1914?
July 28 is the first declaration of war in the chain that became the general war. August 4, 1914, is the date Britain declared war on Germany, which marks the moment the war became general in Europe, but the war between Austria-Hungary and Serbia already existed by then.
Did World War I start in 1917?
No. The United States entered World War I on April 6, 1917, but the war itself had begun in 1914. The year 1917 is the American entry date, not the start date of the war.
When did World War I end?
The fighting on the Western Front stopped with the armistice of November 11, 1918. The main peace treaty with Germany, the Treaty of Versailles, was signed on June 28, 1919.
What was the July Crisis?
The July Crisis was the diplomatic and military escalation between the assassination on June 28, 1914, and the general European war of early August 1914. It included the Austro-Hungarian ultimatum to Serbia on July 23, the declaration of war on July 28, and the declarations of war by Germany, France, and Britain in the first days of August.
Was World War I the same as the Great War?
Yes. The Great War and the First World War are two names for the same war of 1914 to 1918. The name First World War became common after the Second World War made a distinguishing number necessary.
Why do some sources say the war started in August 1914?
August 1914 is when Germany, France, Russia, and Britain were all at war, so it describes the general European war. It is a useful shorthand, but the standard reference start date remains July 28, 1914.
Sources & references
- Encyclopaedia Britannica, World War I: Quick Facts. Checked 27 October 2026 for the date range July 28, 1914 to November 11, 1918, the alternative names First World War, Great War, and WWI, the assassination of Archduke Franz Ferdinand by Gavrilo Princip on June 28, 1914, and the upper range casualty figures of as many as 8.5 million soldiers and 13 million civilians.
- United States Holocaust Memorial Museum, Holocaust Encyclopedia, World War I and its Aftermath: Key Dates. Checked 27 October 2026 for the assassination on June 28, 1914, the Austro-Hungarian ultimatum and declaration of war on Serbia on July 28, the German declarations of war on Russia and then France, the British declaration of war on August 4, 1914, the United States entry on April 6, 1917, the armistice on November 11, 1918, and the Treaty of Versailles on June 28, 1919.
- Imperial War Museums, Outbreak of the First World War, and Voices of the First World War: the declaration of war on August 4, 1914. Checked 27 October 2026 for the June 28 assassination, the July 28 declaration of war on Serbia, the German declarations on August 1 and August 3, and the British declaration on August 4, 1914, together with the context of nationalism, militarism, imperial rivalry, and the alliance system.
- United States Department of State, Office of the Historian, Papers Relating to the Foreign Relations of the United States. Checked 27 October 2026 for the armistice with Germany on November 11, 1918, and the signing of the Treaty of Versailles on June 28, 1919, as recorded in the 1921 treaty restoring friendly relations between the United States and Germany.
