Causes of World War I (1914–1918)
By 1914 European powers were rivals in four ways (remember MAIN):
- Militarism: huge armies and a race to build warships.
- Alliances: two armed groups, the Triple Entente (Britain, France, Russia) and the Triple Alliance led by Germany and Austria-Hungary. A war between two members could pull in all.
- Imperialism: competition for colonies, markets and raw materials in Africa and Asia.
- Nationalism: strong national pride, and peoples inside empires wanting their own states.
The spark: in June 1914 the heir to the Austro-Hungarian throne was assassinated in Sarajevo. Within weeks, alliances turned a local crisis into a European war, which spread to colonies around the world.
How the wars were fought: total war and new technology
World War I
On the Western Front, armies dug long lines of trenches. Machine guns and artillery made attacks very costly, so the front hardly moved for years. New weapons included poison gas, tanks, submarines and early aircraft. In 1917 the USA joined, and revolution took Russia out of the war. An armistice ended the fighting on 11 November 1918.
World War II
WWII was a war of movement: tanks with aircraft support, battles at sea and in the air, and fighting in Europe, North Africa, Asia and the Pacific. Radar, codebreaking, jet engines and finally the atomic bomb (Hiroshima and Nagasaki, August 1945) changed warfare.
Total war
In a total war a country uses everything: factories make weapons, food is rationed, women take on new jobs, colonies send soldiers and supplies, and propaganda keeps people supporting the war. Civilians become targets too, through bombing of cities, blockades and occupation.
From one war to the next: causes of World War II (1939–1945)
- The peace treaties of 1919 (Versailles): Germany lost land, its army was limited, and it had to pay reparations. Many Germans felt humiliated.
- The Great Depression (from 1929): mass unemployment made people turn to extreme parties.
- Dictators and aggressive nationalism: fascism in Italy, Nazism in Germany, militarism in Japan. They wanted new land by force.
- Aggression and appeasement: Japan invaded Manchuria (1931) and China (1937), Italy attacked Ethiopia (1935), Germany took Austria and Czechoslovakia (1938–39). Britain and France gave way to avoid war, and the League of Nations could not act.
When Germany invaded Poland on 1 September 1939, Britain and France declared war. In 1941 the Soviet Union and the USA joined after being attacked, and the war became truly global, including the war in Asia and the Pacific with fierce resistance movements in occupied lands. Germany surrendered in May 1945, Japan in August 1945.
The human cost and the Holocaust
WWI killed about 15–22 million people. WWII killed about 70–85 million, more than half of them civilians. In the Holocaust, Nazi Germany murdered about six million Jews, along with Roma, disabled people and others. Occupied peoples in Europe and Asia suffered forced labour and massacres, and many resisted through underground movements and partisan fighting. A famine in Bengal in 1943, worsened by wartime policies, killed about three million people.
These crimes led to new ideas in international law: war crimes trials (Nuremberg and Tokyo), the word genocide and a convention against it (1948).
Results: a new world order
| After World War I | After World War II | |
|---|---|---|
| Peace body | League of Nations (1920): no army, USA never joined, failed in the 1930s | United Nations (1945): Security Council, wider membership, peacekeeping |
| Empires | German, Austro-Hungarian, Ottoman and Russian empires collapsed | European colonial empires began to end: India 1947, then much of Asia and Africa |
| Powers | Europe weakened, USA rising | Two superpowers, USA and USSR: the Cold War |
| Rights | Minority treaties, women's vote in several countries | Universal Declaration of Human Rights (1948) |
Other lasting results: the welfare state in many countries, European cooperation that later became the European Union, and the nuclear age.
Key formulas and definitions
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Worked examples
1. Give two similarities and two differences between the world wars.
Similarities: both were total wars involving colonies and civilians; both ended with a new peace organisation. Differences: WWI was mostly static trench war while WWII was a fast war of movement; WWII killed far more civilians and ended with atomic bombs.
2. Explain how the end of WWI helped cause WWII.
The 1919 treaties left Germany angry and in debt. When the Depression hit, people backed Hitler, who promised to overturn the treaty. The League, weakened from the start, could not stop his aggression, and appeasement let it grow until 1939.
3. Why did the UN work better than the League of Nations?
The UN included the big powers (USA and USSR) from the start, had a Security Council that can order sanctions or send peacekeepers, and grew to almost every country. The League had no army, lacked the USA and needed unanimous votes.
4. How many years separated the end of WWI and the start of WWII, and why is that period called the interwar years?
1939 − 1918 = 21 years. It sits between the two wars and was shaped by the first and led to the second.
Common mistakes
- Saying one assassination "caused" WWI; it was the spark, the deep causes were MAIN.
- Thinking the wars were only European; both involved Asia, Africa, the Pacific and soldiers from the colonies, including India.
- Mixing up the League of Nations (1920) and the United Nations (1945).
- Forgetting civilians: in WWII more than half of all deaths were civilians.