Hitler's best chance was to conquer the "rest of the world" outside of the Americas, which he and Japan had the power to do, absent vigorous American intervention. The plan would be to conquer what I call the Euro-As-Af land mass.
Put another way, Hitler had to deprive America of a "critical mass" of world power. In both my unpublished book, Axis Overstretch, and a Second World War "take-off" on Civilization II, I hypothesized that the Axis would win if they ever got 50 percent or more of the Wwrld'sworld's industrial capacity (at least before America got the atomic bomb).
In my computer game, there were three other "powers" besides America opposing the Axis: Britain (counting the Commonwealth), the Soviet Union, and China plus a bunch of neutral countries (Spain, Turkey, Iran, etc., and four "cities"countries in Latin America.) Basically the Axis win if they conquer twothree out of three;four; say the Soviet Union, plus China and all the neutrals.
North America plus South America had just under 45% of the world's industrial capacity in 1941, according the Paul Kennedy in "the Rise and Fall of the Great Powers." America needs to retain "neutral" Latin America plus one other power (Britain, the Soviet Union, a conquered Japan, or "Greater China" (all of China plus Southeast Asia) to survive.
To quote from "Axis Overstretch," "As powerful as was the United States of America, she could not survive alone in a world full of enemies. She would even have a very precarious existence if her only friends were in the Western Hemisphere." Hitler's way to win was to "lock out" America from the Eastern Hemisphere.