During WW1 and WW2, Russia/the USSR was considered a nation with vast manpower reserves. Yet, it had a rough population parity with the United States. However, the United States never had the same designation? Why is this? Thanks for any responses!
In 1913, the German population was 65 million, That of the United States approximately 91 million, and Russia was roughly estimated at 170 million. I include Germany as a comparison because in wartime strength is relative. The USA was only about 50% greater in manpower than Germany, but Russia had a two and a half to one manpower advantage. Moreover, the actual deploy-able manpower against Germany for the United States was constrained by available shipping, whereas Russia was often fighting on it's own territory or near its borders and had fewer logistical contraints.
So leaving aside questions of bias, wartime propaganda, and effectiveness of various political systems at mobilization which I'm not qualified to address in detail, Russia was in fact very populated.
The situation on the eve of WWII was slightly more even in terms of population, but the same basic points apply.