Poisonous air and sabotage

The Maraki's planet has a low oxygen content (10%) and high carbon monoxide content of 3000 ppm. This is unfortunate, because not only is it hard to breathe the air, the carbon monoxide will kill any human in 30 minutes. Substitute any other airborne poison as you wish.

People can't breathe the air. Public opinion doesn't like it when they send in the killer bots to extinguish Maraki settlements. The Maraki can and will sabotage any equipment sent down to extract extremely valuable resource A. If the extractors spend enough money on force fields or electric fences and robotic guard dogs to protect their operation, they will be losing money.

Ultimately, companies and governments keep thinking they can make peace with the Maraki or economically protect their extraction sites. Ultimately, these efforts are doomed to open warfare or lack of profit.

This is basically the plot of Avatar.