This chapter explores the significant impact of Nigerians in participating in World War II on the intensification of nationalist efforts and the call for decolonization in Nigeria. It starts by debunking accounts that downplay the role of British colonies in the war and demonstrates that even without the participation of the United States of America, the war would have still been a global affair. It highlights how Nigerians, especially traditional rulers, helped boost the morale of Nigerians to participate in the war and even pledged economic support in terms of kernel production. This was because the British colonies created a sense of solidarity with the British Empire. The chapter is motivated by the following question: what events could have happened throughout the war to have warranted this giant shift in attitudes toward colonialism in the country? This question is answered by tracing the history of Nigeria’s participation in World War II, the effects of the outbreak of war on British colonies, and events that generated the resolve for total self-rule in the aftermath of the war. Taking advantage of the great economic losses and human lives by Britain in World War II, the British’s imperial power and control over its territories became threatened.