What caused Douglas to help pass the Kansas-Nebraska Act?

He thought he could stop the Southern states from seceding, if he could get Congress to allow the people of each new state to vote on the slavery question.

It might have worked, if a lot of states were voting at the same time.

But when it was tried, only in Kansas, that thinly-populated territory became a magnet for terrorists from both sides to intimidate voters. The result was called 'Bleeding Kansas'.