and have lots of the best weapons you can get.
and that's not even actually that hard for anyone with elementary highschool chemistry. birdshit (keep pigeons) charcoal (build a charcoal kiln, it has many uses not the least of which cooking) and sulphur (which is used to inhibit mold on brassicas). voila, make appropriate devices, probably need to find some magnesium. well, aluminium and iron filings will work, just need some goop to stick it to some cord.
uh oh, i just told you a bomb recipe!
trebuches are pretty easy to make too, just rot down some animal carcasses, and voila, bring all the dirty varmints with diseases to the party.
what else is there. hmm. see, those indians needed science. that's how the relatively peaceful europe produced conquerors.
and yeah, as sun tzu explains, using unconventional warfare techniques to acquire weapons from the armories of the enemies is the correct way to do it. stealth, distractions, most important is scouts, you need scouts creeping around as close to the enemy as possible and relaying that information as quickly as possible to the planners.
also, it really reinforces the point. you can win with soft war and unconventional techniques, under some circumstances, but generally, when that fails, you have to have blades, projectiles and incendiaries, and men trained to use them, as well as men trained to make them.
there is no way to overthrow a dictatorship without breaking some eggs, burning some houses down and knocking down bridges.