The pershing was the largest US Tank of WW2 and only US heavy tank. It only saw service in limited numbers in 1945 and used technology stolen from German tanks. It had little impact on the war due to its late entry.
Russia
By the British in World War.
At the outbreak of World War 1, Germany had the largest army among the European powers.
When World War I broke out in 1914, the Russian Empire had the world's largest standing army, with approximately 1400000 soldiers on active duty
Germany
Russia
Yes, it was invented by a colonel of the British Army.
The US built Sherman medium tank.
Russia
The largest "Army" of World War 2 was the Allied Force sent on D-Day (Invasion of Normandy) and the other largest army was the Russian forces that went against the Nazis. Japan had a huge force too but a large majority of them were killed on the islands and in sunken ships.
Pakistan and India War of 1970 (Pakistan Won)
They were introduced during the first World War. (Which went from 1914 to 1918)