My understanding is that the two-handed technique formally only dates back to the 1950’s when Sheriff Jack Weaver popularized it in competitions. It’s called the “Weaver Stance” and it’s still pretty popular in competitive shooting, though it’s been somewhat superseded by what’s called the “modern technique”.

The Weaver Stance is basically holding the gun two handed. You hold the gun in your dominant hand while the other hand wraps around it and supports it. You place the opposite foot (if you’re holding the gun with the right hand, then the left foot) forward and the other foot back and at a 45 degree angle, kind of like the boxing stance. In this position, the feet provide good stability and the hands provide steady support for the gun, so you can be accurate.

In the old days, formal training for shooting was rare, people mostly learned on their own. Any formal training came from military service, and the military used rifles, not handguns. Only officers were issued handguns - but as personal defense weapons, not for combat. They were for emergencies, when you have to pull the gun and shoot fast, you don’t have time to aim. You might very well shoot one-handed in such cases, especially if your other hand is busy with your horse’s reins.

Handguns were mostly used at very close range, so aiming isn’t as important. In fact this style was called “point shooting” where you don’t aim through the sights, you sort of treat the gun as an extension of your arm, and just point it like you’d point a finger. People would sometimes file down or remove the sights, because they had a tendency to snag in the holster when the gun was pulled.

Lack of formal training, expensive ammunition, the intended use (mostly self-defense at short range) – all of these things factored in, so it really was quite common back in the day to shoot one-handed. There are records of gunfights from those times where people are described as steadying their handgun on the forearm of the other hand, so even when there was time for a careful shot, two-handed grips still weren’t that common.

Of course the lack of formal training also means that there was a lot of variety, different people trying out whatever worked for them, so we can’t say that nobody shot two-handed. Probably many did. But the kind of uniformity we see these days when people attend shooting courses and watch shooting videos and there’s a large cadre of formally trained ex-police and ex-military sharing their knowledge just wasn’t common.