The period of time from from the early part of the 21st century until approximately 2050 is known to most historians as "Twilight". Details of the period are sketchy at best, due to the loss of the information infrastructure, along with so much else.
The available evidence suggests that a number of factors pushed the world towards chaos, including shifting weather patterns, political instability in the United States and Russia, expanding terrorist threats, and a hungry world edging towards 7 billion souls.
The shifting weather patterns turned some breadbasket regions into dust-bowls, while deserts bloomed under torrential rains. Famine marched across the globe, and armies with it. At first, the armies were refugees, but as conditions worsened, the refugees were joined by national military units, and their militia brethern.
At some point in the period there was a limited nuclear exchange between Russia, China, and the United States, though the cause is still unknown. Most of Europe and Asia, along with the American East and West Coast, was badly battered, and the consequent destruction of transportation, power and information infrastructures plunged the rest of the world into famine and despair.
France and Japan were among the few nations that retained any sort of infrastructure, and were the first to emerge as whole nations after the war. Japan retreated into isolationism in order to rebuild, but France reached out, first to it's colonies in Africa and South America, and then to the nearby European nations, using the resources it controlled to help the other nations rebuild, and establishing it as the leading nation in the recovery.