The Radical Republicans were the driving force behind several legal changes that allowed African-Americans to gain more rights in American society. This made life for white farmers in the south much more difficult. Here are two examples:
1) 14th amendment- This stated that all individuals born on American soil were citizens. This granted all the rights that white citizens had to African-American citizens.
2) 15th amendment- This gave former slaves and all black men the right to vote. This negatively affected the white south, as the newly freed slave population now had significant political power.