The first choppers were built in America, and were an outgrowth of the milder customization trend that had originated after WW2 when returning soldiers and others began modifying cars and motorcycles, frequently to improve performance in top-speed races on dry lake beds in Southern California and similar desolate spaces such as unused airstrips in other parts of the country, or on the street for street racing. These early modified motorcycles were known as "bobbers", and there are many common features between bobbers and choppers, with choppers differentiated being more radically modified, and especially by having the frame tubes and geometry modified ("chopped" by welding) to make the bike longer.