What was used to discourage the protesters involved in the montgomery bus boycott?

It was used to discourage protesters: violence against the boycott leader, arrest of the boycott leader, appeal of a federal court decision that supports the boycott.

Explanation:

The black population of Montgomery decided to boycott the city buses, ending its boycott only when the law of segregation of races in public transport was revoked. The boycott would financially cripple the bus company, attract tens of thousands of Protestants to demonstrations, present to the country a young charismatic leader named Martin Luther King Jr. and would spark a movement that would spread to Little Rock, Greensboro, Raleigh, Birmingham and, for end, to Congress. Parks would become a heroine, endowed with the Presidential Medal of Freedom, and a shining example of how a single act of challenge can change the world.

But that's just part of the story. In response to the boycott, white opponents decided that they should stop the boycott and so caused acts of violence against the boycott leader, the arrest of the boycott leader, and appeals to stop a federal court decision that supports the boycott.

the doctrine of nullification recommended that states living inside the union have the one-sided, inalienable ideal to void any law made by the national government that could be esteemed illegal.

the united states was shaped based on a general agreement among its individual states. hence, it is inferred that under the hypothesis of invalidation, since the states are the establishment of the union, they have the ability to referee and disprove unlawful laws.