Consequently, the party developed new principles, welcomed the aid of the War Democrats, and found it advisable to drop its name and with its allies to form the Union or National Union party.

It was this National Union party which in 1864 nominated Abraham Lincoln, a Republican, and Andrew Johnson, a Democrat, on the same ticket.
Lincoln's second Cabinet was composed of both Republicans and War Democrats.

When the war ended, the conservative leaders were anxious to hold the Union party together in order to be in a better position to settle the problems of reconstruction, but the movement of the War Democrats back to their old party tended to leave in the Union party only its Republican members, with the radical leaders dominating.
In the South the pressure of war so united the people that party divisions disappeared for a time, but the causes of division continued to exist, and two parties, at least, would have developed had the pressure been removed.

Though all factions supported the war after it began, the former Whigs and Douglas Democrats, when it was over, liked to remember that they had been "Union" men in 1860 and expected to organize in opposition to the extreme Democrats, who were now charged with being responsible for the misfortunes of the South.

They were in a position to affiliate with the National Union party of the North if proper inducements were offered, while the regular Democrats were ready to rejoin their old party.