All settlements and encampments made use of fire so it is not unlikely that they just found each other in that way through smoke. Then, the native American popu

All settlements and encampments made use of fire so it is not unlikely that they just found each other in that way through smoke. Then, the native American population was prepared to handle Europeans militarily, but not from an immunological standpoint. Many conquests were achieved by amplification through local tribes (e.g: fall of Tenochtitlan, largest native settlement was achieved through a force composed of only 4% Europeans, the rest were Tlaxcalans). Incans were contacted during a civil war. The fiercest resistance was offered by the Mapuche tribe in southern Chile (Arauco War, which ended in 1810). Then, life hasn't evolved to become invisible to predators, it has just evolved to survive. e.g: grass hasn't evolved to become invisible to goats. Then, a predator cannot survive if all the preys die. If they're too efficient at killing or too large in numbers they eventually exhaust their food source, just like the cuckoo birds cannot do their trick in every nest and some parasites are better off by not killing their host.