"I have an idea for this planet which will have indigenous sentient inhabitants that have a low tech ceiling and are going to begin resisting human colonization after it becomes apparent that human technology will have an adverse effect on their environment. What is a realistic time frame for such a war?"

-Malcolm

With similar technology, but radically divergent colonization strategies, Spanish-speaking and English-Speaking colonists tried their hands at some very similar aboriginal groups. Highly centralized lower-tech, mass societies, like the Inca and Aztec were easily toppled and fell quickly. However, peoples who had not transformed the land into something easily managed by the agrarian Spanish and English tended to last a long time.

Against the Spanish, people like the Calusa and Apache lasted from 250 to 300 years, that is 10 generations of combatants. More advanced English-speaking enemies took out the Apaches in 50 years and enemy Indians—the mixed-race Seminoles—drove the Calusa and Timucan to extinction in a single generation.

These examples basically highlight what works and what doesn't when colonizing a new habitat. We are seeing a 2-generation English solution to indigenous resistance and a 10-generation Spanish one. Hell, there are still Amazonian Indians beating the shit out of trespassers and uploading the disciplinary pictures online.

The fail-safe English strategy is in three phases: Do not invade like the Spanish, but buy rights to a coastal plot of land. Take some time to learn the local politics and play the inlanders off against your coastal neighbors. By all means import drugs to degrade the cultural cohesion of your new neighbors!

Do not try to enslave the locals, bring your own slaves—maybe automated or bio-tech generated clone slaves for your novel, then have these slaves wage war on the ecology—just trash it.

When the locals attack your slaves for killing their habitat your slaves will fight to defend themselves and fare poorly, which will build in them a sense of hatred for the natives. If 9 of ten slaves die and the 1 remaining slave hates the natives with a passion, you have tempered a fine moral cadre upon which to build a deluded nation of "free" slaves. While they die in droves, you pay your allies in the hinterland to murder the females and young of your enemies.

Bring more slaves and repeat as needed. Most tribes go at the first stroke. The real badass tribes can be worn down by using them to fight the major tribes, which generally take two wars to wipe out. Then you sic your slaves on the remaining badass tribesmen who trained them to fight and clear the slate.

This is pretty much a failsafe system, which worked repeatedly in every one of the original 13 colonies.

I would suggest an original privatized system along the Spanish lines [essentially a feudal economy, let's say small companies establishing independent stations], which can be used to establish backstory and a history of contact between the races, which is then superseded by a larger scale corporate effort that behaves more along English lines.

Silberberg did a nice aquatic version of this in the Face of the Waters.

If you like the idea of indigenous bio-tech instead of mechanical technology, check out Harry Harrison's West of Eden trilogy for an excellent example.

There is also the option of having a storm planet, in which the colonists would try to tame the very weather that the inhabitants tap into for their power source, causing friction in that manner.

Oh, by all means, bring in slaves of very different types, because eventually, it is just going to be you and them and you want them to have someone to hate besides you!

Good luck, Malcolm.