War in the sense of the 20th Century, and in relation to the Canadian Army, describes a state of armed conflict in which weapons and lethal force are used to attempt to resolve the conflict.

Canada was an active direct participant in several wars in the 20th Century:

• Boer War 1899-1902

• First World War 1914-1918

• Second World War 1939-1945

• Korean War 1950-1953

• Gulf War 1991

The termination dates of the wars did not end military participation; for example, Canadian soldiers were still serving in Siberia in 1919, and occupation forces remained in Germany in 1946 and in South Korea until 1955.

Canada also participated in other conflicts, notably the fighting in the former Yugoslavia during their civil war in the 1990s; however, Canada did so ostensibly in a peacekeeping role although some soldiers did see combat (notably at Medak Pocket.)

While not strictly adhering to the definition of an armed conflict, the Cold War is also cited as an example of a war in which Canada was an active direct participant.