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

The phrase "the war to end all wars" is most famously associated with World War I. This label was used because, at the time of the war's conclusion in 1918, many believed that the scale and devastation of such a conflict would prevent future wars. The widespread destruction and loss of life led to the hope that the unprecedented violence would be a defining moment in world history, making nations more focused on diplomacy and lasting peace.

The sentiment encapsulated the disillusionment many felt following the war, as it became clear that World War I did not achieve its goal of lasting peace; in fact, it set the stage for further conflicts in the future. This deep yearning for peace and resolution underscored the importance of World War I in international relations. The other conflicts mentioned did not carry this label or similar connotations.