Answer:
The Kansas-Nebraska Act was a law passed in the United States in 1854 that organized the territories of Kansas and Nebraska. It was proposed by the Democratic Senator Stephen Douglas, and was passed with the support of President Franklin Pierce. The law opened the Kansas and Nebraska areas to settlers and allowed railways to be built in the area. At the same time, the attitude of the new territories to slavery was left to the people of the area to decide, which overturned the previous Missouri Compromise of 1820.
The decision to leave the issue of slavery to the residents of the area was ultimately fatal. When both opponents and supporters of slavery rushed into the area just to vote for slavery, the situation became violent. Armed groups assembled by supporters and opponents of slavery terrorized the area for four months before federal troops entered the area.
Politically, the law was a huge defeat for Douglas and President Franklin Pierce, who supported him. The future president of the United States, Abraham Lincoln, who opposed slavery, managed to use the law to his advantage.