The causes of World War I are usually taught as MAIN: militarism (an arms race and rigid war plans), alliances (Europe split into two armed blocs), imperialism (rivalry over colonies and influence) and nationalism (Slav nationalism in the Balkans above all). Those were the long-term conditions. The trigger was the assassination of Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, in Sarajevo on 28 June 1914 by Gavrilo Princip, a Bosnian Serb nationalist. In the July Crisis that followed, Austria-Hungary, backed by Germany, declared war on Serbia; Russia mobilised to support Serbia; Germany declared war on Russia and France and invaded Belgium; and Britain declared war on Germany on 4 August 1914.

This guide takes the causes in the order an exam answer needs them: the long-term conditions, the crises that tested them, the five weeks of July, then the argument about blame.

MAIN in one table

MAIN is a revision device, not an argument. It names the conditions; it does not say which one mattered most, and a top answer has to. Here is what each letter actually means, with the evidence you are expected to know.

Two details students often get wrong. Italy was in the Triple Alliance but did not join Germany in 1914; it entered the war on the Allied side in 1915. And the Triple Entente was not a binding military alliance for Britain. Britain had no treaty obliging it to fight for France or Russia, which is why its decision in August came down to Belgium.

The Schlieffen Plan, the hinge between causes and war

Germany's war plan, drawn up by Alfred von Schlieffen and revised by Helmuth von Moltke, assumed a war on two fronts. Russia was huge but slow to mobilise, so Germany would knock France out first, in about six weeks, by sweeping through neutral Belgium, then turn east.

That plan is why the crisis escalated the way it did. A war with Russia, under this plan, meant attacking France first, and attacking France meant invading Belgium, which the great powers, Britain, France and Prussia among them, had promised to keep neutral in the Treaty of London of 1839. The historian A. J. P. Taylor called the result "war by timetable": once Russia mobilised, German generals believed every day of waiting was a day lost.

The crises that tested the system

Before 1914, the same powers came close to war several times and stepped back. Each time, someone drew a lesson that made 1914 harder to stop.

• First Moroccan Crisis, 1905 to 1906. Kaiser Wilhelm II visits Tangier to challenge French influence in Morocco. At the Algeciras Conference, Britain backs France and Germany is isolated. The Entente grows stronger.
• Bosnian Crisis, 1908 to 1909. Austria-Hungary annexes Bosnia-Herzegovina, which it had occupied since 1878. Serbia, which wanted Bosnia's Serbs, is furious. Russia, weak after losing to Japan in 1905, backs down under German pressure. Russia resolves not to back down again.
• Agadir Crisis, 1911. Germany sends the gunboat Panther to the Moroccan port of Agadir. Britain again stands with France. Germany gains some land in central Africa but is humiliated.
• Balkan Wars, 1912 to 1913. Serbia and its neighbours drive the Ottoman Empire almost out of Europe, then fight over the spoils. Serbia nearly doubles in size. To Vienna, Serbia now looks like a mortal threat to an empire full of South Slavs.

The July Crisis, day by day

This is the part exams ask about most, and it is easiest to learn as a calendar.

Two things stand out when you lay it out like this. First, the gap between 28 June and 23 July: nearly four weeks in which Austria-Hungary planned, with German backing, rather than reacted in anger. Second, how fast the last week moved. From Austria's declaration of war on Serbia to Britain's declaration on Germany took seven days, and most of that speed came from mobilisation timetables.

How historians weigh the causes

The question you will be set is rarely "list the causes". It is "how far was Germany responsible" or "were the alliances the main cause". Here are the positions you should be able to name.

The Treaty of Versailles, 1919. Article 231, the "war guilt clause", made Germany and its allies accept responsibility for the loss and damage of the war. It was a peace term written by the winners, not a historical verdict, but it framed the debate for decades.

Nobody meant it. In the 1920s and 1930s many writers shared the blame around. The British wartime leader David Lloyd George later wrote that the nations "slithered over the brink" into war. This view puts the system, the alliances and the timetables, at the centre.

Fritz Fischer, 1961. The German historian Fritz Fischer, in the book published in English as Germany's Aims in the First World War, used German archives to argue that Germany's leaders deliberately risked, and to a degree sought, a European war to make Germany a world power. It caused a storm in West Germany and put German responsibility back at the front.

Christopher Clark, 2012. In The Sleepwalkers, Clark argues that responsibility was shared, that Serbia, Russia and France also made choices that pushed towards war, and that the leaders were "blind to the reality of the horror" they were bringing about. Margaret MacMillan's The War That Ended Peace (2013) also stresses choices made by individuals, arguing that war was not inevitable.

A strong answer does three things: it separates long-term conditions (MAIN) from the short-term trigger (Sarajevo) and the decisions in between (the blank cheque, the ultimatum, Russian mobilisation, the Schlieffen Plan); it picks a main cause and defends it; and it names at least one historian who disagrees.

The mistakes that lose marks

• Saying the assassination caused the war. It was the trigger. Other assassinations had not led to war. The answer has to explain why this one did.
• Treating MAIN as four equal causes. Examiners reward a judgement about which mattered most and how they connected.
• Saying Italy fought with Germany. It stayed neutral in 1914 and joined the Allies in 1915.
• Saying Britain was bound by the Entente. It was not. Belgium and the 1839 treaty gave Britain its stated reason, alongside fear of a Europe dominated by Germany.
• Getting the order of declarations wrong. Austria on Serbia (28 July), Germany on Russia (1 August), Germany on France (3 August), Britain on Germany (4 August).
• Calling the Black Hand the Serbian government. It was a secret society with links to Serbian military intelligence. How much the Serbian government knew is still argued over.

A scene plan for a five minute video

The causes are a chain, so the video works best as a map of Europe that fills up. A recurring drawn map, with the two blocs coloured in and a fuse running across it, carries the whole argument. How to explain a map in a video covers keeping a map readable across scenes.

1. A map of Europe in 1914, empty. The question on screen: why did a murder in Sarajevo become a world war?
2. The alliances drawn in: two colours, the Triple Alliance and the Triple Entente, with dates on each link.
3. Militarism: two navies of battleships growing side by side; the Schlieffen Plan as an arrow through Belgium.
4. Imperialism: Morocco, twice, with Britain stepping in beside France.
5. Nationalism: the Balkans zoomed in, Serbia doubling in size, Bosnia shaded inside Austria-Hungary.
6. Sarajevo, 28 June: a single car on a street.
7. The calendar from the table above, one date at a time, each declaration lighting a country.
8. Belgium invaded; Britain's line drawn in last.
9. The historians: Versailles, Fischer and Clark as three labelled positions on one line, from "Germany's fault" to "shared".

Make your own version for class

Turn the topic into a question first. How to make a timeline video for history class covers choosing a thesis and events, and the companion piece the Cold War, explained visually uses the same structure for 1945 to 1991.

1. 1

   Pick a thesis you can defend

   One sentence, such as: alliances made a general war possible, but German decisions in July 1914 made it happen. It decides which events and historians you keep.

2. 2

   Choose 10 to 12 dated events

   Take them from the tables above and check each date against your textbook. Write one line on what happened and one line on how it supports or challenges your thesis.

3. 3

   Write one paragraph per scene

   Open with the question and thesis, include at least one historian who disagrees, and end with your judgement. At 150 spoken words a minute, 750 words is five minutes.

4. 4

   Paste the script into openCanviz

   Choose Keep my wording and a target length. Painted or poster styles suit the period. Keep the map of Europe as a recurring element so the blocs fill in scene by scene.

5. 5

   Check every date, name and border

   Pause on each scene. Drafted drawings can misplace Serbia, spell Bethmann Hollweg wrong or draw 1914 borders as they are today. Fix any scene in the editor before you hand it in.

If you are revising this for an essay exam rather than presenting it, the best way to study for a history essay exam shows how to turn these causes into practised paragraphs.

Common questions

What were the four main causes of World War I? Militarism, alliances, imperialism and nationalism, often remembered as MAIN. They were long-term conditions. The immediate trigger was the assassination of Archduke Franz Ferdinand in Sarajevo on 28 June 1914.

Who killed Franz Ferdinand and why? Gavrilo Princip, a 19 year old Bosnian Serb, shot him and his wife Sophie in Sarajevo. Princip belonged to a group that wanted Bosnia freed from Austria-Hungary and joined with Serbia, and the group was armed with help from the Black Hand.

Why did Britain join the war? Germany invaded Belgium, whose neutrality Britain had guaranteed in the Treaty of London of 1839. Britain also feared a Europe dominated by Germany and wanted to stand by France and Russia, though it had no treaty forcing it to.

Was Germany to blame for World War I? Historians disagree. The Treaty of Versailles blamed Germany and its allies. Fritz Fischer argued German leaders deliberately risked a European war. Christopher Clark and others argue responsibility was shared, with Austria-Hungary, Russia, Serbia and France also making choices that led to war.

What was the blank cheque? Germany's promise, given on 5 and 6 July 1914, to support Austria-Hungary in whatever action it took against Serbia. It encouraged Vienna to send a harsh ultimatum rather than settle the matter quietly.