World War I:
1. Austria-Hungary and Germany: Following the assassination of Archduke Franz Ferdinand of Austria in 1914, Austria-Hungary issued an ultimatum to Serbia, expecting them to accept several conditions that were seen as harsh and provocative. When Serbia did not fully agree, Austria-Hungary declared war on Serbia, triggering a chain reaction of alliances and declarations of war that led to the outbreak of World War I.
2. Imperialist Ambitions: Tensions had been building between European powers due to imperial rivalries, the arms race, and alliances formed between countries. Britain, France, Russian, and Germany had differing interests in territories and power, and these conflicts contributed to the wider war.
3. Militarism and Nationalism: Rising militarism and nationalism played significant roles. Governments and militaries focused on building up their armed forces and fostering nationalistic sentiments. This created an atmosphere where conflict could easily escalate.
World War II:
1. Germany: Under Adolf Hitler's leadership, Germany pursued aggressive expansionist policies, leading to the invasion of Poland in 1939, which is considered the start of World War II. Hitler's desire to expand German territories and create an Aryan racial state through the conquest of other nations was a primary factor in the war's instigation.
2. Appeasement Policies: Some historians argue that the appeasement policies of Britain and France towards Germany in the 1930s allowed Hitler to gain momentum and emboldened his aggressive actions. The unwillingness to confront him earlier contributed to the eventual escalation of the war.
3. Imperial Rivalry and Expansionism: Japan's desire for territorial expansion in Asia, Italy's pursuit of territories under the Fascist regime, and the Soviet Union's objectives influenced to the geopolitical tensions that led to the war.
It's important to note that wars as complex and multifaceted events, often with interconnected causes and influences, making it challenging to pinpoint a single instigator. The factors mentioned here are some of the key points that are commonly discussed in the historical analysis of world wars.