The UN has plenty of ways and regulations and crap to see this coming and know the solution. If one country in the UN attacks another in the UN, then it would be the attackers fault and all countrys have to unite against them. Now if for some odd reason the other countries decided that attacking russia or china isent what they want, they would drop from the UN because they wouldent be able to hold up their end of the bargan. And with that comes the collapse of the UN because if they cant even follow their own rules then the UN wouldent exist anyway. Now even if the UN falls through because of a new war, countries have close alliances with many different countrys. All countries usually depend on other countries for import/export or some other reason that will directly effect and hurt their economy so they would want to get involved. You break a rule or regulation while in the UN and thats like insulting every country in the UN and they take action against you. There are a handful of countries in the world powerful enough to start a world war of epic porportions by declaring war on another one. What? this topic is about world war two ? oh... Umm... Yeah Germany screwed itself...