How did Franklin Pierce's position on slavery affect the situation in Kansas?

Pierce believed in the Constitutional right of a state to allow slavery but he was not pro-slavery. Therefore it seemed reasonable to let the people in a territory to decide if they wanted to allow slavery instead of the using the Missouri Compromise procedure to admitting states in pairs, one slave and one free.

However, Nebraska was anti-slavery so unless Kansas voted to be a slave state, the balance would be upset and this is what caused all the trouble in Kansas.