Ratville is the neighbor city and rival city of Petropolis, is the hometown of Verminious Snaptrap (both the Snaptrap's dad as the Snaptrap we see throughout the series from the first episode). Initially would be founded with Petropolis as a single city, with two founders (one of them was a rat), when he said that in that city would be considered forbidden cheese, the other founder refused that idea, and so were founded Petropolis and Ratville separately, began to have many conflicts and attacks. When in the mid-'80s, Petropolis and Ratville would sign a peace agreement, comes an inhabitant of Petropolis Ratville to return to declare war on this city, we talk about Verminious Snaptrap Senior, with his wife and children (including Verminious Snaptrap Junior, the Snaptrap that we see throughout the series). His children grew up and he saw on Snaptrap Jr. his great heir of evil and the post of leader of DOOM (his father was the founder and former leader of DOOM). Snaptrap did his in Petropolis, drawing the attention of TUFF, founded while Ratville still held conflicts with Petropolis. In the episode of the third season of TUFF Puppy, Return to Ratville (first episode in which it appears and is mentioned Ratville) Snaptrap goes Ratville to call all Ratville's inhabitants to invade Petropolis, so Dudley and Kitty are disguised as rats, to prevent the invasion.
Trivia: - It's Obvious that Ratville (TUFF Puppy), is a copy of Shelbyville (The Simpsons) (more details in Return to Ratville).