There are about ten countries on this planet with nuclear warfare capabilities: United States, China, Pakistan, India, North Korea, Great Britain, Israel, France, Russia, and Germany.
United States, Great Britain, and Israel are a triumvirate. Willing to fight for eachother in an instant.
China and North Korea have an obscure yet tight-knit underground alliance.
France and Germany have been enemies since the dawn of their creation. Yet as of lately, their hatred has been dissolved. They are now edgy yet close allies.
India and Pakistan despise each other.
Russia is solo on this one...
Ultimately, The United States will always have quarrel with Non-Democratic nations. China being the biggest threat to America, will be their number one enemy by default.
Eventually, China will initiate some type of agreement with North Korea that will create an open alliance. Which in turn, will give North Korea the confidence to continue their nuclear arms program. This will then aggravate The United States and put them under pressure. The United States will continue to send diplomats as well as increase espionage in North Korea. If the United States continues to have a Warmonger president like Bush, then more severe actions will be taken.
The United States will declare an ultimatum to North Korea, which will ultimately state for North Korea to disengage from all nuclear development. If North Korea refuses, The United States will embark into another great crusade to oust a foreign government with military force. Inevitably, North Korea will decline the ultimatum.
The United States will be in shock of North Korea's sudden refusal. A second ultimatum would be declared to North Korea. Yet again, they will decline. The United States would have no other choice but to begin the invasion.
The Wings of Death will begin to spread. Shrouding the Earth in shadows and dust...