Given the following passage  "In the early 21st century, Republican voters control most of the state, especially in the more rural and suburban areas outside of the cities; Democratic strength is mostly confined to the urban cores of the four major cities, and is particularly strong in the cities of Nashville and Memphis. The latter area includes a large African-American population. Historically, Republicans had their greatest strength in East Tennessee before the 1960s. Tennessee's 1st and 2nd congressional districts, based in the Tri-Cities and Knoxville, respectively, are among the few historically Republican districts in the South. Those districts' residents supported the Union over the Confederacy during the Civil War; they identified with the GOP after the war and have stayed with that party ever since. The 1st has been in Republican hands continuously since 1881, and Republicans (or their antecedents) have held it for all but four years since 1859. The 2nd has been held continuously by Republicans or their antecedents since 1859.",  answer the following question. Note that the answer is present within the text.  Question: What was the base of the few historically Republican districts in the South?
A:
the Tri-Cities and Knoxville