I need ideas for alternatives to the Missouri Compromise of 1820 that would have been acceptable to all sides.The immediate ending of slavery is...

This is a very tough question and I'm not sure I have a good answer, but here goes.

I'd like to start by stating the problem.  You have a balance between free and slave states so that means the Senate is equally split so each side can essentially veto any action it doesn't like.  But now Missouri wants to become a state and you have to figure out what to do with it and the rest of the area obtained thru the LA Purchase.

As you say, you can't just ban slavery in the whole Purchase.  Neither can you require that it be allowed.  Neither of those will work.

I suppose you could go with the popular sovereignty idea that ended up in the Kansas-Nebraska Act in '54 -- where you let each new state or territory decide about slavery for themselves.  But that's problematic because no matter what Missouri decides, it upsets the balance.

I suppose you could draw the line somewhere other than 36-30, but that doesn't really change anything all that much.

I think if I had to answer this I'd do it in these steps: lay out the problem, state some alternatives, say why those wouldn't work.  Conclusion: the people who made the Compromise did the best they possibly could.

I can see myself asking this question hoping you'd come to that conclusion.  Do you think your prof might be doing that?