Final answer:
World War I was the war that led to increased job opportunities for black men in factories in the North, initiating the Great Migration. The need for labor during World War II also provided further job opportunities and led to anti-discrimination measures like Executive Order 8802 and the FEPC.
Step-by-step explanation:
The war that contributed to opening up job opportunities for black men in factories in the North was World War I. This era marked the beginning of the Great Migration, where nearly 350,000 African Americans moved from the rural South to the North in search of better employment and to escape the oppressive segregation laws. The need for laborers in the defense industry during World War II further enhanced these opportunities as African American men and women filled vacancies left by those who went to war. Executive Order 8802 and the creation of the Fair Employment Practice Committee (FEPC) in 1941 were significant in safeguarding these new workers' equality and access to jobs against discriminatory practices.