In our times the US Army is by far the strongest army, far surpassing every other military. But compared to that how was the situation in 1939? Would the general power be as equal, lower or even higher than Nazi Germany at the beginning of the World War? As Germany wanted world domination.
The US Army was only the 19th largest in the world, by numbers, in 1939. A lot of people seemed to have enjoyed making the comparison to Portugal's army, which was larger at the time. However, military strength does not lie in the number of soldiers alone. The army could grow so quickly and become so powerful in just a few years because it derived from a populous nation bolstered by economic strength, natural resources, manufacturing capacity, and territorial isolation from the immediate dangers of foreign armies. So when asking how "strong" the US Army was in 1939, one might note that it was relatively small in numbers, with far less material support as well, but it is important to recognize that the Army was attached to a nation with the potential to expand its strength, in due time, if needed. More importantly, one can never underestimate the intellectual strength behind the American Army, which fueled the research and development that would lead to its competitive edge in war.