To play devil's advocate, suppose we re-evaluated our own behavior and "stepped down" from that position. It would be great if nobody stepped in to fill that void, but they would without a doubt.
That hypothetical situation is so far divorced from reality that it's impossible to say anything useful about it. Right now, the US spends more on its military than the next seven countries combined. A world in which those tables were turned would look very little like ours.