I believe it was actually settled a little earlier than that. The rebellion/war started in 1899 and we quickly learned the short comings of rounds that did not begin with a 4. The 1873 Peacemaker was reissued because the 1892 Colt .38 wasn't working. The M1909 revolver was issued in 45 and then we finally got smart and lucky and got the best pistol in the world for combat use, JMB's M1911. The official primary sidearm issued for 75 years, the M1911A1 is still issued for some units after 110 years of service, with only one minor design change since it was invented.
Civilian versions have seen a few more modifications of the design, with some (like STI's 2011 series) even handling almost as much ammo as a 9mm Glock but in a caliber that works.