Write any one cause of first world war.

One of the primary causes of the First World War was the rise of extreme nationalism and the complex system of secret alliances that divided Europe into two hostile camps.

By the early 20th century, European powers were bound by various treaties, such as the Triple Alliance (Germany, Austria-Hungary, and Italy) and the Triple Entente (France, Russia, and Great Britain). These alliances meant that a localized conflict could rapidly escalate into a general European war. When the assassination of Archduke Franz Ferdinand occurred in 1914, the alliance system triggered a chain reaction, forcing major powers to mobilize their armies in support of their respective allies, thereby transforming a regional Balkan crisis into a global conflict.