I believe that the main reason Police used a Revolver here for most of the 20th Century is because we wanted them to be armed with an effective cartridge that they could shoot accurately. Reliability was also key, and nothing is more inherently reliable than a Colt or S&W DA Revolver.

Many Police Officers could not handle or shoot effectively the 1911's and while they are very reliable, not as much as a Revolver is. Clearing jams from an Auto-loader under fire is a learned and practiced skill - not easily done in a gun fight. If you get a "dud" with a Revolver, simply pull the trigger again - not so with an Auto. Most Auto's are "less safe" when carried with a round in the chamber and a DA Revolver is way more safe in that condition.

As far as Europe is concerned, up until recent times it is my opinion that their Police have been "under - armed" with small caliber weapons. I do not think a .25, .32 or .380 cartridge for Police is adequate and they obviously did. Be that as it may, the smaller caliber pistols are a lot easier to handle, shoot with better accuracy do to less recoil, and they felt it worked for them.

Now the European PD's are mostly armed with 9mm Pistols as are our own PD's. They offer good reliability, high capacity, manageable recoil, effective cartridges are now readily available, and they can be carried relatively safe ready to fire - assuming the PO's get proper training.

So that's my take on your post.