How did the newly opened territory of Kansas become a battle ground for the issue of slavery?

Kansas became a battleground for the issue of slavery due to the Kansas-Nebraska Act of 1854 which allowed residents of the territories to decide whether they would allow slavery or not (popular sovereignty). This led to clashes between pro-slavery and anti-slavery settlers, known as "Bleeding Kansas," as both groups sought to influence the outcome of the territory's status as a free or slave state.