The USSR fought Germany, Italy, Romania, Hungary, Croatia, Bulgaria all at once, as well as Ukrainian, Baltic, Russian and other defectors from within the USSR, in addition to Waffen-SS volunteers from practically all over Europe including Sweden, Denmark, Norway, the Netherlands, Belgium, France, Bosnia, even Poland and more. The Wehrmacht also integrated volunteer units, such as the Spanish Blue Division (47.000 fighters).
Most of these forces were trained and equipped by Germany, some like the Italians could rely on extensive defence industries of their own.