First published in 1973, The Causes of War examines why nations enter armed conflict and why they eventually make peace. Drawing on international wars from 1700 onwards, Geoffrey Blainey argues that conflict often begins when opposing governments disagree about their relative strength. Each side may expect victory or believe that fighting will secure a better outcome than negotiation. In this account, leaders’ assessments of military and diplomatic power are central to understanding the outbreak of war.

Blainey considers explanations involving economic pressures, military preparations, national ambitions and apparent accidents, questioning whether any single factor can account for the historical record. He also examines why some wars last longer than others and why peace agreements become possible. His central argument is that war and peace should be studied together: hostilities can end when opposing sides develop more compatible estimates of their strength and prospects. Later editions expand the discussion of twentieth-century conflicts and nuclear warfare.