Final answer:
The term of enlistment President Abraham Lincoln requested from state governors to supply soldiers for the Union army was ninety days.
Step-by-step explanation:
The Union army initially did not permit African Americans to serve, but over time and especially following key policy changes like the Emancipation Proclamation, African Americans did start joining and serving in significant numbers. The response after the fall of Fort Sumter was such that President Abraham Lincoln called on the states to recruit 75,000 men to serve in the Union army for a period of ninety days to suppress the rebellion. As the war continued and it became clear that the conflict would not be resolved quickly, the term of soldiers' enlistment was extended beyond the initial scope.