* Imperialism: The competition between European powers for colonies and resources was a major factor in the outbreak of World War I.
* Nationalism: The rise of nationalism in Europe, particularly in the Balkans, led to increased tensions between countries.
* Militarism: The build-up of arms and military forces by European powers created a sense of insecurity and fear, making it more likely that conflicts would escalate into war.
* The Assassination of Archduke Franz Ferdinand: The assassination of Archduke Franz Ferdinand, the heir to the Austro-Hungarian throne, by a Serbian nationalist was the spark that ignited World War I.
World War 2
* The Rise of Fascism: The rise of fascist regimes in Europe, particularly in Germany, Italy, and Japan, led to increased aggression and a disregard for international law.
* The Treaty of Versailles: The harsh terms of the Treaty of Versailles, which ended World War I, left Germany feeling humiliated and resentful, and contributed to the rise of Nazism in Germany.
* Appeasement: The policy of appeasement, which involved giving in to the demands of aggressive powers in order to avoid war, failed to deter Germany and Japan from pursuing their expansionist goals.
* The Invasion of Poland: The German invasion of Poland in September 1939 is generally considered to be the start of World War II.