Shortly after the birth of the Mega-Corps came an attempt to keep the profit focused country sized corporations in check. The Intercosmic Space Treaty Organization grew as an attempt for independent governments to come together to not only prevent themselves from being completely absorbed by the Mega-Corporations, but to also offer some form of neutral ground where the Mega-Corporations, approved governments, and non-planetary entities could join.
As of yet no "aliens" (other than certain Pillar representatives) have made their presence known to the ISTO, however the standard of setting the ISTO as a intercosmic space treaty organization instead of limiting the design and structure of the group to planetary (or government) based affairs ensured that the continued development of space stations, terraformed planetary structures, and even moon colonization by both governments and mega-corps would fall under the ISTO's purview.
The ISTO does have a human army, as well as has designed its contractual organization that all mega-corps and governments that wish to be represented within the ISTO must make their standing armies available in the interests of the continuation of humanity's survival. The ability for mega-corps to choose their Pillar assignments to the ISTO also inadvertently provides another field of competition between the mega-corps and another venue of corporate espionage.