Why did Lincoln refuse to accept the separation of southern states?

Lincoln did not refuse to accept the separation of the Southern states. In fact, he offered several options for the secessionists to return to the Union, including the Crittenden Compromise, which would have guaranteed the continued existence of slavery in the Southern states. However, the secessionists rejected all of Lincoln's offers and instead attacked Fort Sumter, thus starting the Civil War. Lincoln then issued the Emancipation Proclamation, which freed all slaves in the Confederate states, in order to weaken the Confederacy and bring an end to the war.