As America (And England I suppose?) hit the beaches of Normandy... AGAIN... France would use a tactical nuclear weapon to destroy the American forces. The situation escelates until France and it's European allies are nothing but radioactive vapor and England and America are crippled beyond repair. In the economic freefall that follows, Eastern Europe and Central Asia will fall in behind Russia and Southeast Asia, Africa, and South America would fall in behind China. Non-Chinese allied states in East Asia (Japan, Taiwan, South Korea) and the pacific (New Guinea, Kingdom of Hawaii, Australia) will create an anti-comintern pact to hold off against their rivals and will immediately start building a nuclear deterrent.
In the Middle East Israel will no longer be receiving copious amounts of American military or financial aid and their neighbors will no longer be receiving aid to not attack Israel, leading to a massive economic crunch. War will soon follow and Israel will be forced to use their nuclear weapons in self defense.
In North America, refugees pour into Canada, solving their manpower problem and Canada becomes a major power. A North American Union is created between Mexico, the United States, and Canada, with Canada as the leading nation. The NAU is too busy rebuilding to exert influence on the rest of the world, but the potential is there and it's really a very amicable solution.
The destruction of the breadbasket (or at least the infrastructure that carries the food to the tables) and the global cooling from a nuclear winter leads to massive famine across the world, many minor wars break out and hydroponic gardening becomes popular and necessary in urban areas.
Oh, and when the nuclear exchange starts, George Bush attempts to flee the country on Air Force One, but is instead arrested for treason and sentenced to life in prison, he currently resides in prison.
