After WW1, Germany could not design or produce submachine guns due to the Versailles treaty. To keep producing them, German companies and designers exported the patents and tooling to other nations such as Switzerland. The M20 was a SIG produced version of Bergmann's submachine gun, created for exports on this new and expansive post war weapons market. They were sold and produced in many nations, including in China (Tsing Tao, which we released as a different mod), Japan (Type Be), and Finland.
These weapons were used in the different conflicts of the interwards period and in WW2 by several countries.