Their national website claims that Mongolia contributed quantities of food and wool comparable to US lend-lease and over 1/2 million horses to their Soviet allies. I’d never heard of this before, but if true, it would mean that Mongolia certainly pushed above its weight, given a population < 1million.
Because Mongolia had a mutual assistance pact with the Soviet Union since 1936, would Mongolia not have an obligation to declare war om Nazi Germany when Germany invaded the Soviet Union?
Perhaps Stalin was afraid that Japan might use a Mongolian declaration of war against Germany as a pretext for war, since the Tripartite Pact obligated them to help Germany if it was atacked by a country with whom they were not at war.
From what I can tell (and there is very little info freely available) Mongolia never declared war on Germany. That being because, as far as I can infer, USSR preferred that it instead use all troops to reinforce the Mongolia-Manchuria border after victory at Halhin Gol. Some crazy percentage of its population was mobilized, but I don’t have the number here. It appears that Soviet Asian units that arrived to the Eastern front in late 1941 may have been ethnic Mongols, but were not Mongolians (save that some sources mention Mongolian Military College students in the USSR who fought on the Eastern Front). In late 1945, Mongolia declared war on Japan and helped the USSR with its invasion of Manchuria.