How about Virginia abolishes slavery in the 1840's, which leads to an earlier secession of the Southern States in the mid 1850's in fear that without Virginia, their cause is doomed.
Robert E. Lee begins the war as a Colonel in the Union Army, but by the last year of the war 1859 he is a famous General and responsible for some of the Union's greatest victories that reunified the nation. In 1860 he asked by the Democratic Party to run as their candidate, which he does and wins. Thus in 1861 Robert E. Lee is sworn in as the 16th (?) President of the United States.