Often the ad networks for non-Western countries are different, so you really need to look to domain-specific partners.

For example, AdMob may be a great choice for your app in the US and Europe, but a terrible choice for distributing an app in China.

Expect to see more Western ad networks acquiring or partnering region-specific ad providers (I speak from experience, my employer owns both a popular EU/US mobile ad network and one of the larger Chinese networks).