You can apply to a number of airlines all over the world. The question is: Do you really want that? Agencies not only take a part of your pay (the contract fee from the airline), but they also give you some sort of protection and a service. If you apply for an airline where there is an environment different to the western system - politics, law, way of life -, there is always the risk that you will run into problems. When you get your pay directly from an agency and you can talk directly to a person in English, you are protected to a certain extent.
Good luck,
Dani