The emancipation proclamation affected the union's civil war efforts by?
1) allowing the union to turn its attention away from slavery
2) increasing the number of troops who could join the union
3) forcing southern slaveholders to free enslaved people (not the answer; already tried)
4) forcing northern african americans to join the union army

2) Increasing the number of troops who could join the Union.

Explanation:

The Emancipation Proclamation was an executive order issued by Abraham Lincoln on January 1, 1863. This order stated that when a slave escaped the control of the Confederate government, either by running away or by advancement of the Union troops, the slave became free. Eventually, when the Confederate Army surrendered, this emancipation applied to all slaves. The proclamation allowed more people (former slaves) to join the Union and help in the war.