Another fairly large topic that probably could take hundreds of pages of writing and discussion and hours of research, but my opinion is that once Lincoln was elected, the only way war would be averted would have been for either side - north or south - to have completely sacrificed their basic principles and beliefs, be they state's rights, the government's right to control slavery in the territories, or if states had the rights to seceed. From all I've read and heard, I just cannot see where any compromise was possible without one side totally giving up their basic philiosphies.
Slavery either could be stopped from going into the territories by the federal government or it could not. No "sometimes it can, sometimes in can't" idea would work.
Likewise, states either could seceed at their own desire, or they could not. Again, no "sometimes they can, sometimes they can't" idea would be feasible.
My belief is that once Lincoln was officially elected as President, South Carolina was determined to seceed (or attempt to seceed, if you prefer) and that only a true sacrifice of the principles on which the Republican party had campaigned could change that. Even then President James Buchanan was not weak enough to give up Fort Sumter or to say that secession was legal. He did not attempt to stop it, but at the very least maintained the status quo until Lincoln officially took office. In other words, Buchanan's leadership was bad, but "it could have been worse."