A major challenge for the americans in world war 2 was that

building an army and rapidly training troops

Explanation:

1. failure of appeasement

2. building an army

3. rapidly training troops

4. converting to a war time economy

your answer is

to dominate europe

and i know for a fact it can't be the others

wisdom

explanation:

the fact that that the teachings on the cosmic order comes from, or through, the heart center