Which conflict was referred to as "the war to end all wars"?

The conflict commonly referred to as "the war to end all wars" is World War I. This phrase was popularized during and after the war, particularly in the context of the hope that the massive scale and horrific carnage experienced during World War I would lead to a lasting peace and prevent future global conflicts. The term reflects the sentiment of many at the time, who believed that the widespread destruction and loss of life would make nations more committed to diplomacy and collective security moving forward.

World War I was unprecedented in its scale and impact, involving many of the world's great powers and resulting in significant geopolitical changes. The idealism surrounding the notion of ending wars was later challenged by the reality of subsequent conflicts, particularly World War II and various Cold War engagements, which demonstrated that the end of one major conflict did not necessarily guarantee the absence of future wars. This recognition of the ongoing struggle for peace and the complexities of international relations would ultimately lead to a more nuanced understanding of warfare and diplomacy in the 20th century and beyond.