The war was the result of a competition for world dominance with the Reich and Japan on one hand and the United States on the other. The U.S was the only non-Axis dominated or aligned country in the world.
Germany was the first country to develop nuclear weapons. Using the same technology it used to build V-1 and V-2 missiles in the Second World War and defeat Britain and the Soviet Union, the Germans developed "robot bombs" to attack and destroy key American cities, including Washington, DC and Philadelphia. The US was able to launch attacks on the Reich, and cause it significant damage. Nonetheless, America was decisively defeated, losing a third of its population, probably mounting to several tens of millions.
After the war ended, the Reich began exterminating the Jewish and Negro populations in the United States with large massacres taking place in New York City and Los Angeles. Some white American population assisted in these massacres.
With the former capital of Washington, D.C. reduced to a nuclear wasteland, the American capital was moved to Omaha in the Mid West where a pro-Nazi administration was established. The Wehrmacht maintained bases in New York, Chicago, St. Louis and Omaha itself.
Under the Reich, the United States was forced to pay war reparations in the form of an annual tribute. This became an important source of income for the Reich's economy. When the United States was either unable to pay this tribute or was late doing so, the Wehrmacht used terror tactics like destroying a city or plundering the countryside to speed up the process. The Americans nonethless did their best to hide the resources they had from the German government.
Germany's second victory over its enemies was a propaganda victory of the Reich. In Reich schools, youth were taught by their teachers that the German Reich had won for several reasons including its technological superiority and the general lack of intelligence found in Americans.