From Lincoln's letter to Horace Greeley, Aug. 22, 1862:
"If there be those who would not save the Union unless they could at the same time destroy slavery, I do not agree with them. My paramount object in this struggle is to save the Union, and is not either to save or to destroy slavery. If I could save the Union without freeing any slave I would do it..."
Although Lincoln did believe:
"...my oft-expressed personal wish that all men every where could be free."
it was obviously not his main motivation in the Civil war.