I doubt we would have been up to taking on the Rome-Berlin-Tokyo Axis.
It wouldn't have occurred, because the USA would not have intervened in World War I, and Germany would have won it. Hitler would have never came to power.
Why would the USA not intervene in WWI? Because as two different countries, it wouldn't have had the military might that it possessed in our time line, and would have been much more shy about getting involved in such a conflict.
No USA intervention, No Hitler coming to power.