Explain why is it that these ultra-defenceless natives resisted European incursions in today's United States and Canada until late in the 19th century,
The land was awful and there was no reason for the US to conquer them all at once, but rather as waves of settlers came and the US had to “evict” the natives from the native land. The US and Britain had no impetus to go ahead and conquer vast swaths of native lands without their own settlers there or wanting to be there.
even using European mercenaries and vice versa during this four century period, or why there's a 30 year period of massive cultural exchange between Tainos and Spaniards between 1492 and 1519 when Cortes's invasion of Mexico begins.
Spain obviously upon discovery of the New World acted like any other nation would: tepidly though excitedly. The thirty years are because they didn’t immediately go “argh we want conquer grrrrr” but instead only did so once certain stories reached them (from said cultural exchange with the Taino) and as they consolidated the Caribbean. Also note that it was an individual that had the idea of invasion, and it was later sponsored by Spain when he asked for it. It wasn’t a state-led affair at all, so the thirty years waiting for a crazy-enough and cruel-enough individual make even more sense. No reason to invade the Mexica when the island natives are putting up enough problems as is.
In fact, why is it that the Portuguese colonised Brazil extremely gradually, why the Guyanas needed to be conquered by the Dutch, the southern Antilles by the Dutch, the English and the French, and why the Inca Empire wasn't fully conquered until 1572, over 40 years after Pizarro's campaign started?
What point are you even trying to make? Colonization takes time, because colonization takes people. Theoretically, it would have been materially possible for it to happen faster, but because it is an inherently political and capitalistic procedure, people had to be convinced to get rid of their entire livelihoods and lives in the Old World to take a chance in a new one. Of course it wouldn’t happen immediately. Also, no one ever said Native Americans, north and south, didn’t resist and resist well, like you seem to be implying about what we’ve said.
We shouldn't talk of "effective ways of prevention" in the first place because Native Americans weren't any more susceptible to European diseases than Europeans themselves.
Aaaaaand this pseudoscientific bullshit again.
I’m not even saying anything more to this, this has already been discussed and debunked at length in another thread, and this entire belief of yours stems from a misreading of a book of essays, which never claims what you’re getting from it, instead saying that the natural susceptibility was drastically increased by certain political and military pressures on the part of the Europeans, something that makes sense. Instead, you have twisted it to say that only those pressures had anything to do with it, which is, of course, bullshit.
If so, how do you explain the Old Believers in Siberia who had no contact with the Old World trading network and were almost completely isolated, matching the same criterion as the Native Americans? Once discovered by a Soviet team of scientists, they almost all died (within a very short period of time) of respiratory diseases which did not affect the Soviets nearly as badly.
