Why were so many people involved in world war 1?

World War I saw widespread involvement due to a complex web of alliances, militarism, nationalism, and imperial ambitions among the major powers of Europe. The assassination of Archduke Franz Ferdinand of Austria-Hungary triggered a series of events that activated these alliances, drawing countries into the conflict. Additionally, colonial empires brought in troops and resources from around the globe, further expanding the war's reach. The war ultimately involved nations from multiple continents, leading to a truly global conflict.