which president advocated for relatively quick and easy ways to bring the south back into the union was it lincoln or radical republicans

Abraham Lincoln

Explanation:

Abraham Lincoln wanted to be lenient to the South and make it easy for southern states to rejoin the Union. He said that any southerner who took an oath to the Union would be given a pardon. ... Under Lincoln's plan, any state that was readmitted must make slavery illegal as part of their constitution.

regarding the law, the 15th amendment was specifically designed thinking in the rights of black free men.

even though ratified on february 3, 1870, the promise of the 15th amendment would not be fully applied for a long time.poll taxes and literacy tests would allow southern states disenfranchise african americans. only in 1965 the voting rights for african americans would be actually able to vote in the south.

in 1965, president johnson signed the voting rights act, which aimed to overcome legal barriers that prevented african americans from voting as it was guaranteed by the 15th amendment to the u.s. constitution.