This is not true of everywhere that was colonized. See Africa, or India. It would not be possible, even with very great tech advantage, to sustain millitary campaigns so far from europe without a safe port to base supplies etc, not to mention the manpower etc. These were very much made possible by what was essentially a standard playbook of allying with some natives against others, and using trade imbalance, violence, strongarming and other things to turn those "allies" into protectorates, and eventually colonies

Right. I am not saying diseases were a factor in every conquest. Just refuting parent saying that conquest is "only possible" through infighting. It's not - overwhelming technological advantage or disease are also sufficient even against a united culture.