What even is Pax?

Maybe I just missed it when I was playing in the campaign, but what even is Pax Amarta? Are they a separate military coalition, if so of what country’s? Terrorist Group? Mercenary group? Their voice lines give off the impression of non professional soldiers by saying things like “enemy tank” compared to nato’s “enemy Armor” (Military’s such as the US are very deliberate with wording, you are expected to refer to your rifle as your weapon, not gun) however in the first mission of the campaign NATO was planning on handing over a base to PAX so it gives the impression that PAX does have authority and is not just a terrorist group.