For fucks sake. The 40th United States Congress held together to override Presidential vetoes for the following reasons:
1) It was an overwhelmingly Republican and/or Union-centric body adamant about preserving the political gains from the Civil War, including maintaining the establishment of the Freedmen’s Bureau, the establishment of Reconstruction in the southern states, and the passage of what would eventually become the 14th Amendment
2) Andrew Johnson was a Southern politician with southern sympathies that Lincoln incorrectly tabbed as a means to show his desire for unity among the states. He was despised by Republicans and Northerners alike and went out of his way to stoke the flames of that animosity, in the hopes of appealing to Southern Democrats. Which failed miserably.
There has never been an over-arching theme of national unity in this country, and even if we came close, it certainly wouldn’t be found in the years immediately following the American Civil War.