How did the newly opened territory of kansas become a battleground for the issue of slavery?

Two opposing governments were established: those who wanted slavery to be legal in Kansas and those who did not.

Explanation:

In 1854, the U.S. Congress passed The Kansas-Nebraska Act that repealed the Missouri Compromise (1820) that prohibited slavery north of latitude 36°30', created the territories of Kansas and Nebraska and allowed people in those territories to decide for themselves whether to allow slavery within their borders under the principle of "popular sovereignty."

Soon after the Act was enacted, pro-slavery and anti-slavery whites began to settle Kansas in order to participate in the first election that would determine if Kansas would be a free or a slave state. However, once the first election was held, anti-slavery settlers did not accept the outcome alleging that it had been electoral fraud. Afterward, the anti-slavery people held another election but pro-slavery people refused to vote, and both "governments" created two legislature within the territory. Soon enough, with the establishment of these two opposing governments: pro-slavery and anti-slavery, the newly opened territory of Kansas became a battleground for the issue of slavery: violence, raids, assaults and civil confrontations increased within its borders, the death toll rose, and other elections were called but none of them were accepted.