Final answer:
People in Africa, Canada, India, and Australia participated in World War I principally because they were part of European colonial empires. The war was a manifestation of the imperialistic endeavors of these powers, and colonial subjects contributed in the hope of achieving political autonomy and self-determination.
Step-by-step explanation:
The primary reason that people in Africa, Canada, India, and Australia participated in World War I was that they were part of European colonial empires. These colonial nations were involved in the conflict largely due to the imperialistic policies of the European powers that controlled them. Colonies provided troops and resources, and in some cases, their own territories served as battlegrounds. Although colonial troops fought valiantly alongside their European counterparts, many did so in the hope that their service would lead to increased political autonomy and the right to self-determination.
Moreover, participation in the war brought about significant changes in the colonies. African soldiers, for example, who fought in World War I, later leveraged their contribution to demand more political power and autonomy after witnessing international discourse on self-determination. However, the redrawing of colonial borders after the war often neglected the ethnic and cultural lines within these societies, leading to further complications.