We pretty much withdrew from the world stage after WWI. The Axis powers discounted us as any kind of threat even though we demonstrated in WWI that Americans have the will to battle and are good to excellent soldiers and marksmen.
However, in the intervening years the Italians, Japanese and Germans took measure of us and saw a weak country that didn't want to be on the world stage. Remember the Japanese thought that after wrecking the Pacific Fleet at Pearl Harbor that we would immediately sue for peace and Japan would be able to continue it's goal of the creation of the "Greater East-Asia Co-Prosperity Sphere".
They under estimated us.
We are currently is the same type of drawdown (with the Active force being reduce to pre-WWII numbers). Again, all that does is embolden our enemies. Our current political leaders learned nothing from the Cold War.
This was said a long, long, long time ago, but it holds true yet today.
Si vis pacem, para bellum.