What was a major cause of rising international tensions in early 1900 World War 1?

A major cause of rising international tensions in the early 1900s leading to World War I was the complex web of alliances and militarism among European powers. Nationalism fueled rivalries, particularly in the Balkans, where ethnic groups sought independence from empires like Austria-Hungary. Additionally, the arms race and competition for colonies heightened distrust and aggression among nations. The assassination of Archduke Franz Ferdinand in 1914 acted as the catalyst that ignited these existing tensions into a full-scale war.