American Strategy: WW2

 Members of the
War Department General Staff
and the War Plans Division,
November 1941

On September 1, 1939, the day when the WW2 broke out with Hitler’s invasion of Poland. The US (country along with armed forces) was pretty much divided on the possible course of action suitable for the US.It was

• Creating isolation and unilateral defense of entire North America if it was attacked either by 1 or all of the AXIS forces. 
• Shift of US defense concentrations in the Western Pacific to protect its interests (esp. Philippines)
• Unilateral defense of the entire Western Hemisphere. This was because of the Monroe Doctrine in which it stated that “any efforts by European nations to take control of an independent state in North or South America would be viewed as "the manifestation of an unfriendly disposition toward the United States “. It also resulted in the Organization of American States 
• Other options were the grand alliance with Great Britain and France as in World War I and offensive operations with them against Germany and Italy while temporarily assuming a strategic defensive position against Berlin’s Japanese ally
• Alliance with and support of Britain and France against Germany but a projection of U.S. offensive power to the Pacific against Japan so as to protect U.S. Far Eastern as well as Pacific interests—most notably the Open Door in China along with the Philippines—while the British and French allies handled Germany on their own.

These options were discussed in the United States RAINBOW Plans when the planners realized that the United States faced the possibility of war on multiple fronts against a coalition of enemies.

Chicago Daily on FDR's War Plan

Among them was Rainbow 5 which was accepted by both the army and FDR in mid-1941. It was the Europe First or Germany First.

Rainbow 5, destined to be the basis for American strategy in World War II, assumed that the United States was allied with Britain and France and provided for offensive operations by American forces in Europe, Africa, or both

Interestingly RAINBOW 5 had the elements of the plan (RED-ORANGE of the 1920s) which were previously designed to defeat Great Britain in case of a war.