The UN? Hardly, given the Security Council gives Russia a veto - like the USSR had throughout the Cold War. It is blatantly powerless.
The so-called "peace movement"? Yes, they may get upset at Russia, but really some will be glad there is a powerful challenge to the US as the only superpower. The "peace movement" is only interested in surrender of fighting, it would have surrendered East Asia to Japan, continental Europe to Nazi Germany, South Korea to North Korea, just as it surrendered South Vietnam to North Vietnam.
There is only one option - the USA, bolstered by NATO. NATO's rejection of Georgia and Ukraine's membership bids recently was done partly out of fear of "upsetting Russia". There are other reasons to withhold, but still progress membership. Georgia is paying the price for it.
It isn't quite a new Cold War, but Russia is flexing itself. If it gets away with effectively annexing parts of Georgia, it may try again against Ukraine, it almost certainly will claim more of the Arctic, and may treat Belarus more as an extension of itself - particularly if Lukashenko can be deposed.
The only way to deter this effectively is for states which are friendly to the values of freedom, liberal democracy and open transparent government to be aligned with NATO - and for NATO's implicit nuclear umbrella to be extended to them.
This wont impress the left, many of whom miss the USSR - but it is in all our interests once and for all to contain Russia's ambitions. Russia is today a fascist state, with a governing party that faces no real challenge, a media either owned by the state or those compliant with the state, and a leadership aggressive, militaristic and with little hesitation to spill blood. If it wants to be treated as a civilised country it needs to treat its neighbours with respect, even if most of its citizens are comfortable with being pushed around by the bullies who run it.