How did congress try to keep the union together ?

Congressional leaders prodded Lincoln into making overtures to South for a peaceful resolution and to put an end to the hostilities. Lincoln's problem always remained that recognition of the South in any manner would under the Union. So, Congress did the only thing it could do. Go along with Lincoln. Congress did this by enacting laws that gave Lincoln the authority to confiscate property of Confederates, to declare and use captured slaves considered to be contraband as instruments in the war effort including their enlistment in the Union army. See the Confiscation Acts of 1861 and 1862, and the Militia Act of 1862. Congress passed the Crittenden-Johnson Resolution (1863) which stated its position in the War and on the question of slavery: to put down the rebellion and not interfere with slavery. Congress also indemnified Lincoln by suspending the ancient writ of habeas corpus. See Habeas Corpus Suspension Act 1863. In areas not under Union control; Congress admitted a partial state as part of the Union. West Virginia was admitted to the Union on June 20, 1863.