With all of the different races in Guild Wars 2, it has to be wondered how so many of them were unknown to humans during the original Guild Wars. A recent interview with ArenaNet’s narrative designer Ree Soesbee answered exactly that question, explaining that many of these races simply lived in places otherwise untraveled by humans but wound up forced into new spaces due to the Elder Dragons. That’s kind of the theme of the whole, other races and Elder Dragons.
For example, Soesbee makes it clear that while the death of an Elder Dragon theoretically strengthens the remaining Elder Dragons, there’s still far too little known in the world about how the Elder Dragons even work to be sure what would happen if only one remained. Similarly, the minions of the Elder Dragon Zhaitan such as Tequatl are still evolving and becoming more powerful as a result of his death. It’s a brief interview, but it may well help tie up a few niggling lore questions you have (like why the Tengu still aren’t friendly).