In one paragraph, explain the main causes of World War I.

World War I was primarily caused by a complex interplay of several long-term factors and a critical short-term trigger. Militarism fueled an arms race and glorified military power, creating an environment ripe for conflict. A tangled web of alliances divided Europe into two opposing blocs—the Triple Entente (France, Britain, Russia) and the Triple Alliance (Germany, Austria-Hungary, Italy)—meaning a localized conflict could quickly escalate. Imperialism led to intense competition among European powers for colonies and resources, generating rivalries and disputes. Furthermore, fervent nationalism fostered desires for self-determination among ethnic groups and contributed to aggressive foreign policies. The immediate spark was the assassination of Archduke Franz Ferdinand of Austria-Hungary by a Serbian nationalist in June 1914, which set the alliance system in motion and rapidly plunged the continent into war.