From Gamer Limit; Shoot 'em up games started innocently enough. Spacewar shot it's way onto PCs back in the 1960s, and after Space Invaders was released, the rest was history. Galaga and Galaxian would go on to further popularize the genre, and R-Type and Gradius would modernize it. Shoot 'em ups started as casual games. I mean, who hasn't played Galaga?! Eventually, Eastern game studios got their hands on the genre, and changed it forever. Shoot 'em ups were no longer heaven; they were absolute hell.