The next morning, six infantry divisions, two motorized brigades, a paratrooper unit, and hundreds of aircraft, including 186 Heinkel bombers, launched Operation Weser Maneuver. Denmark capitulated. Norway resisted and was crushed. “Once we have the two countries,” Goebbels recorded, “England will be flattened” because Germany could use Scandinavia as “a base of attack.” As for the United States? That country “is of no interest to us,” Goebbels wrote, because by the time the Americans could deliver any material assistance (eight months, in Goebbels’s reckoning) or put boots on the ground in Europe (18 months), the war would be over.
The US didn't especially want to fight Germany on land in Europe, but rather across the Atlantic, a battlefield which played to its strengths. The basic US intent was to keep the Axis from acquiring a beachhead from which it could stage against the US.
If Nazi Germany declared ownership of the American colonies of European countries that it had conquered, US war plans involved occupying them and declaring war on Nazi Germany. It didn't want to have them used by Germany as a staging point for being used against the US; it wanted to force the Axis into a naval war, so that it could leverage its greater industrial power and turn the war into one of naval and air construction, in which it would be able to ultimately overwhelm the Axis.
searches
Oh, this is actually a better source than the one I was looking for.
https://history.army.mil/portals/143/Images/Publications/catalog/4-1.pdf
The Framework of Hemisphere Defense
The Crisis of 1940
Though the United States Army in the summer of 1939 was stronger and better prepared for action than it had been in the earlier 1930's, it was numerically far weaker than the army of any other world power. On the other hand the United States Navy, somewhat favored over the Army in the initial rearmament program, had a strength just below that of Great Britain. While Japan's ominous naval expansion was making protection of American interests in the Pacific an increasingly formidable task, the Navy in general was ready to perform its traditional function of providing the first line of defense in a war emergency. Nor can the military power of the United States in 1939 be reckoned solely in terms of active Army and Navy strengths. Both services had partially trained reserve components, and the nation's industrial might constituted a tremendous military asset. As World War II was to show, the military potential of the United States exceeded that of any other nation.
Sometime during September 1939, when the President was shown a draft of one long-range scheme for military expansion, he is reported to have said: "Whatever happens, we won't send troops abroad; we need only think of defending this hemisphere." The President and his aides likewise foresaw that no serious threat to the Western Hemisphere could arise unless the British and French were pushed to the brink of defeat. In that event the United States would be faced with the grim choice either of supporting Great Britain and France, "as our outlying defense outposts," or of vastly increasing American naval power to "meet the ultimate issue between us and a Russo-German Europe bent on dominating the world, somewhere in the Middle Atlantic." In an informal discussion on 19 September, the President and Assistant Secretary of State Berle
. . . ranged the globe, forecasting the division of Eastern Europe between Germany and Russia, wondering whether Western Asia was also to be divided, and guessing at the chance of an ultimate German foothold in the Atlantic. Both thought that if Germany won the war, Hitler would try to get his hands on the Azores or Cape Verde Islands, as bases for operations against the Americas. But both agreed that the war's main danger to this country lay in the alternative prospects of post-war economic chaos or a world economy dominated by the dictatorships.
The new joint RAINBOW 4 plan was based on assumptions that clearly indicated the dire forebodings of Army and Navy officers at the end of May. It assumed that, after the defeat of Britain and France, the United States would be faced by a hostile German-Italian-Japanese coalition. Its combined naval power, bolstered by portions of the British and French Fleets, would considerably exceed that of the United States. Japan would proclaim its absolute hegemony in the Far East, and might seize the Philippines and Guam.
Germany and Italy would occupy all British and French territory in Africa, and also Iceland. In Latin America, the Germans and Italians would use every means to stir antagonism toward the United States, and they might succeed in establishing pro-Axis governments in strategically located countries. Canada, remaining technically at war with Germany, would occupy Newfoundland, and the United States would have to join with Canada in the defense of Newfoundland and Greenland. Nevertheless, a considerable interval would probably elapse after the British and French collapse before the United States would be drawn openly into war.
The United States planned to counter these threats initially by occupying key British, French, Dutch, and Danish possessions in the Western Hemisphere claimed by Germany and Italy as the spoils of war. Thereafter, its armed forces must be disposed along the Atlantic front of the hemisphere so as to prevent any lodgment by Axis military forces. In the Pacific, every effort would have to be made to avoid open hostilities with Japan; if they began, the United States should base its defense on Oahu and Alaska. The major portion of the United States Fleet would have to be withdrawn from the Pacific and concentrated in the Caribbean area. Though the original RAINBOW 4 concept had contemplated defense of the entire Western Hemisphere, the armed forces of the United States for the time being would have to confine their operations to North America and the northern part of South America (approximately within RAINBOW 1 limits), extending their operations southward only as additional forces became available. While maintaining a defensive position in both the Atlantic and the Pacific, the nation would have to increase its military power as rapidly as possible, with the eventual objective of limited offensive action. In presenting the RAINBOW 4 plan to the Joint Board, the Joint Planners stressed above all the critical situation that would arise if the main elements of the British and French Fleets were surrendered to the Axis Powers. Should that happen, Germany and Italy would soon attain a naval strength in the Atlantic equal or superior to that of the entire United States Fleet. The planners estimated that the Axis nations would require a minimum of six months to recondition and man the surrendered vessels. For the United States, they pointed out, there would be two critical dates in this process: "The first is the date that either the British or French Fleet ceases to function, by reason either of destruction or surrender. The second is six months after that date. . . . The date of the loss of the British or French Fleets automatically sets the date of our mobilization.
[continued in child]