Why didn't lincon free slaves in all of the united states

The Civil War was fundamentally a conflict over slavery. However, the way Lincoln saw it, emancipation, when it came, would have to be gradual, as the most important thing was to prevent the Southern rebellion from severing the Union permanently in two.

Explanation:

The way Abraham Lincoln saw it, emancipation needed to be gradual. He thought this because at the time, the most important thing was to prevent the Southern rebellion from severing the Union permanently in two.