How One Locomotive Controls 100 Others Wirelessly

One engineer sits in a single cab. Behind him, stretching two miles back, are up to a hundred individual locomotive axles spread across multiple engines, none of which he can see, none of which he can touch, and none of which are connected to him by a single wire. He moves the throttle. Every one of them responds within milliseconds. Why does a system this precise run on radio signals the same way your garage door does? And why, if radio works fine, did it take engineers sixty years to actually trust it?