The Need for a Fix to International Conflict

A few days ago, I was reading a news article on the proposed NATO endorsement for a "rapid-reaction force of 4,000 troops" to be deployed to protect Ukraine against Russian rebel forces. I started thinking about all the conflict we have in the world, and what we're doing to stop it. I just cannot understand how countries like Russia can get away with open, repeated, devastating attacks against a smaller nation for entirely greed-fueled incentives (in this case, Crimea's oil fields) while we have international organizations like the UN and NATO who stand by and do absolutely nothing, apart from the occasional economic sanction or sending of troops. It is for this reason that we continue to have corrupt, oppressive governments like the ones in North Korea, Cuba, Libya, etc. and widespread, brutal terrorist organizations like ISIS. Granted, there is a whole host of issues that come with a large international body attempting to prevent conflict in the world; a country has the right to its own sovereignty, and once the UN invades North Korea, what's to stop it from invading any other country? There is also the issue of the UN being composed mostly of the US's troops, who could then use it as a tool for their own world domination. I understand that there's a lot of problems with international conflict resolution, but I still wish there was something we could do other than standing by and imposing ineffective sanctions.