The problem with not getting involved Thriller is that Russia will become even more bold. They paralyze the UN as a veto member of the Security Council. China doesn't care and EU is not strong enough. So that leaves America.
Russia wants its old power and glory back. Look at what they did to Georgia. Now Ukraine. Who is next? At what point is enough, enough?
Problem with withdrawing from the world is that the two other most powerful nations (Russia and China) are not America friendly. If we do and say nothing the eastern Euro nations (Ukraine, Georgia, Uzbekistan, Coatia, Estonia...) will fall one by one to Russian power and influence. The Asian countries ( Thailand, Taiwan, Singapore, Malaysia, Cambodia, Vietnam, Philippines, Japan...) will fall to China. You are already seeing clear steps taken in that direction.
Then China and Russia are each American equals. I do not think they are our enemies yet but I certainly don't think they are friendly.