Early in the 20th century, Germany went to war, lost, and—in accordance with the WWI Armistice Treaty—was forced stop making airplane engines. For Bayerische Motoren Werke (Rapp Motorenwerke prior to 1916), this was a problem. So the small airplane engine maker turned to building farm equipment, household items, and railway brakes until 1928, when it diversified. Taking control of a small automobile factory in Eisenach, Germany, BMW officially became a carbuilding concern.
This is a companion discussion topic for the original entry at https://www.hagerty.com/articles-videos/articles/2018/03/07/6-bmws-you-have-never-heard-of