How did the missouri compromise balance power in congress? 1. slavery was outlawed in all new states, so there was no longer an argument over the issue in congress. 2. missouri and maine entered the union as a slave state and free state, respectively, maintaining the equal number. 3. missouri and maine entered the union as slave states and kept representation equal in the senate. 4. missouri and maine entered the union as free states and kept representation equal in the house.