Given a text, write a compressed version of it in a single sentence.

The firm belief in "manifest destiny" and territorial expansion led ineluctably to the Civil War. As long as the Union was fixed at a certain number of slave states and a certain number of free, both sides could calculate the future.
The firm belief in "manifest destiny" and territorial expansion led ineluctably to the Civil War. Both sides could calculate the future with a certain number of slave states.