What strategic objective contributed to president abraham lincoln's decision to issue the emancipation proclamation?
group of answer choices

by freeing all slaves in the united states, lincoln caused the southern economy to collapse due to a shortage of labor on southern farms.

by freeing all slaves in the united states, lincoln shifted the war's focus from slavery to the economic imbalance between the north and south.

by freeing all slaves in the northern states, lincoln allowed thousands of african americans from the north to serve as soldiers in the union army.

by freeing all slaves in the southern states, lincoln made the war about slavery and caused european nations to resist aiding the confederacy.