The answer is "She was sick of segregation"
In Montgomery, the capital of Alabama, the first rows of buses were, by law, reserved for white passengers. Behind them were the seats where the blacks could sit. On December 1, 1955, Rosa Parks took one of these buses on her way home from work and sat down at one of the places in the middle of the bus. When the driver-white-demanded that she and three other blacks rise to give way to whites who had entered the bus, Parks refused to comply with the order. She remained seated and was therefore arrested and taken to prison.
Rosa Parks' silent protest against segregation spread rapidly. The Women's Political Council organized a boycott of urban buses as a protest against racial discrimination in the country. Martin Luther King Jr. was one of those who supported the action. Activist and musician Harry Belafonte recalls how his life changed after the day King telephoned him to call for support for the action of the woman who became known as the "mother of civil rights movements" in the United States.
