The 7.92x57mm Mauser, aka 8mm Mauser round is a German bullet first used in the G98 Mauser rifle. Other German rifles chambered (Size of the bullet the gun can take) in 7.92x57mm include weapons such as the K98, MG34, MG42, FG42, G41, and G43.
A variant (Different style) of the 7.92x57mm, the 7.92x33 mm "8mm Kurz", was created as an intermediate cartridge intended to be used in urban warfare, as the German army learned from fighting in cities, mainly in Russia after Operation Barbarossa. The 8mm Kurz was used in the STG44 assault rifle. This round, weapon, and concept was picked up and expanded on by the Russians after the war, and this led up to the development of the 7.62x39mm cartridge used in the SKS45, AK47 (and variants), and the RPD light machine gun.
After World War II, Germany was split into two countries, West Germany and East Germany, and both countries stopped using 8mm Mauser weapons. This was because the alliances they made required them to use the same ammunition for all their weapons as their allies. West Germany would use NATO weapons, and East Germany would use Warsaw Pact weapons.