List of wars: 1900–1944

This is a list of wars that began between 1900 and 1944.

This period saw the outbreak of World War I (1914–1918) and World War II (1939–1945), which are among the deadliest conflicts in human history, with many of the world's great powers partaking in total war and some partaking in genocides. Depending on the source consulted, conflict deaths reached an all-time peak in either 1941 or 1942 at 2.96–7.71 million, during the height of the latter conflict.

Besides the aforementioned world wars, a number of smaller conflicts also took place. In Africa, conflicts of this era were mostly fought between European colonial forces on one side and native kingdoms and insurgents on the other, though there are exceptions (e.g. the Italo-Turkish War, as well as intercolonial invasions of German, Italian and Vichy French possessions in the World Wars). Likewise, Southeast Asia saw a large variety of native rebellions against the American, European and Japanese colonial empires, while also seeing the intercolonial Pacific War.

Other parts of Afro-Eurasia, as well as the Americas, saw a wide variety of conventional wars, civil wars, ethnic or political conflicts, revolutions, and small rebellions. Prior to 1940, Australia saw only sporadic conflict as the frontier wars entered its final stages. However, in World War II, Australia became the site of Axis naval activity and air raids.