The .45 ACP wasn't produced until 1911; before the start of World War 1. It was utilized by the American icon; the Colt M1911 and it's variants. It later became the round for other weapons; from other countries.
The .45 ACP; from it's introduction in the 20th century; has remained one of the most popular pistol calibers to be utilized and even after a service of over 100 years; the round refuses to be put to rest. Archaeologists such as Tony Secord; utilizes the .45 ACP in his dual Mauser C96 pistols; customized to his needs.