Why were Union troops stationed in the South after the war ended?

Union troops stationed in the South after the war ended as a part of reconstruction process.

Explanation:

After the civil war, the union government set conditions fro the former confederate states to be readmitted into union marking the beginning of reconstruction. the important conditions were that the states have to accept and ratify the implementation of 13 and 14 amendments which insisted the abolition of slavery.

Presidential election took place in 1876 in which the democrats had won all the public offices but there were secret negotiations that continue which made democrats to accept Hayes to be the president of the south but on one condition and that was to pull all the federal troops that were stationed in southern states and increasing the funds to infrastructural improvements. this deal was accepted by Hayes and hence it was in favor of him.