Who was fending off the monsters before Buffy moved to Sunnydale?

So I’m only 9 episodes in, but here’s two things I don’t understand: pretty much every week, someone either dies or gets attacked, how does the school not get shut down? Second of all, before Buddy came to the school, who was taking care of the monster attacks? The hellmouth would still be active but why hadn’t everyone been killed and the whole town destroyed?