Final answer:
The Kansas-Nebraska Act led to a civil war between pro- and anti-slavery settlers in Kansas.
Step-by-step explanation:
The subject of this question is History, and it pertains to the Kansas-Nebraska Act and its impact on the Civil War between pro- and anti-slavery settlers.
The Kansas-Nebraska Act, passed in 1854, allowed the residents of Kansas and Nebraska territories to decide on the issue of slavery through popular sovereignty. This led to a fierce conflict between those in favor of and against slavery, resulting in a series of violent clashes and incidents known as Bleeding Kansas.
The correct answer to the question is A. Kansas, as the Kansas-Nebraska Act directly led to the violent disputes and eventual civil war in that state.
Learn more about Kansas-Nebraska Act and Civil War