Gangsters continued into the 1940s

Actually, the government or WWII didn't stop the gangsters. They continued into the 1940s, during the War.

That is obvious since mafias still exist today. However, these were the gangs during the Prohibition era which was about 1920 to 1933.

What I also meant was that they were strong after Prohibition as well, but by the 1950s their power was being broke.