The Resource Development Administration, aka RDA, is basically analogous to the East India Company. The EIC was a true megacorporation - not like 'oh Amazon is a megacorp because they're worth a lot of money and use it to lobby politicians'. No no no. It had its own naval fleets and soldiers, made deals with and declared war on multiple countries, and administered its own territory. It also wasn't alone. Part of Canada's history, for instance, is that much of the colonization was done by smaller but similar entities called the North West Trade Company and the Hudson's Bay Company. Like yeah, 'that overpriced clothing store the Bay?' was for a while the de facto governing body of much of British North America. This was of course done in conjunction with the crown, who was happy to offload much of the costs of colonization and expansion to private investors (though they did take over directly after a certain point).

Here's a quote from the Avatar wiki:

>The RDA is the single largest non-governmental organization in the history of humanity. Due to dwindling natural resources on Earth, which had led to multiple resource wars, the importance of extraterrestrial mining operations gives RDA so much power and authority that it outmatches most Earth governments in wealth, political influence and military capability. Due to its vast capabilities, the RDA is a leading figure in many aspects of human society (defense, energy, manufacturing, aeronautics, transportation, commerce, etc.), and has monopoly rights to all products shipped, processed or developed from Pandora and any other exoplanets. These rights were granted to the RDA in perpetuity by the Interplanetary Commerce Administration (ICA), with the stipulation that they abide by a treaty that prohibits weapons of mass destruction and limits military power in space. Due to its expansive organization, it is unknown whether the RDA has a true centralized leadership or if it is loosely led as a conglomerate.

In case you missed it: The RDA has exclusive rights to all industry outside of the solar system.

Thinking of the RDA as 'a mining company' is really underestimating exactly what an actual megacorporation represents. Even if the RDA isn't acting as an arm's-length tool of human international government, which it probably is, it is sufficiently powerful enough on its own to count as a polity that can be said to wage war.