Activision committed to battle royale early and captured a huge audience with its standalone, free-to-play Call of Duty: Warzone. This brings us to our current era, the one I believe is on its way out the door: battle royale.
That was fun for a bit, but then the clock reset and Activision thought, hey, maybe World War 2 would be fun again. When hero shooters hit big, Treyarch responded with Black Ops 3's unique characters and ultimates. There was the era where everyone was super-into modern military shooters, followed by a few years when our boots lifted off the ground and started wallrunning or jetpacking. You can roughly map out the evolution of first-person shooters over the last 1.5 decades with the yearly Call of Duty releases.
