Which best explains how nationalism helped cause world war 1?

Nationalism played a significant role in causing World War I for several reasons:

1. Rivalries and Alliances: Nationalism fueled intense competition among European nations, each seeking to assert its dominance and power. This competition led to the formation of military alliances such as the Triple Entente (France, Russia, and the UK) and the Triple Alliance (Germany, Austria-Hungary, and Italy). Nationalistic fervor within these alliances created a volatile environment where conflicts between nations could quickly escalate into a broader war.
2. Desire for Self-Determination: Nationalism also stirred desires for self-determination among various ethnic groups and regions within larger empires. For instance, in the Balkans, nationalist movements sought independence from the Austro-Hungarian and Ottoman Empires. These aspirations for independence and self-rule led to tensions and conflicts, triggering a chain reaction of events that eventually contributed to the outbreak of the war.
3. Assassination of Archduke Franz Ferdinand: The assassination of Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, by a Bosnian Serb nationalist in Sarajevo in 1914 acted as a catalyst for the war. This event heightened pre-existing tensions between Austria-Hungary and Serbia, leading to a series of diplomatic crises and ultimatums ultimately resulting in the declaration of war.
4. Patriotic Sentiments: Nationalism fostered a strong sense of patriotism and loyalty to one's country, which led to enthusiastic support for the war effort. Propaganda and nationalist rhetoric contributed to the mobilization of large populations for war as people were fueled by a sense of duty to defend their nation's honor and interests.

In summary, nationalism's impact on the geopolitical landscape, desires for self-determination, the formation of alliances, and the strong patriotic sentiments it invoked all contributed to the complex web of factors that led to the outbreak of World War I.