According to wikipedia: Unionist was a political label adopted at various times in the United States by opponents of secession. It was used primarily by Southerners who did not want to affiliate with the Republicans, or wished to win over anti-secession Democrats. For the Presidential election of 1864, the Unionist label was adopted by the Republican Party. The Republicans were joined by many War Democrats, including Andrew Johnson of Tennessee, who was the candidate for Vice President.