That most likely would have happened anyway. Even without Columbus's voyage, the existence of ships capable of intercontinental travel would have led to an an e

That most likely would have happened anyway. Even without Columbus's voyage, the existence of ships capable of intercontinental travel would have led to an an encounter that would have played out much the same way: decimation of the population by foreign pathogens from a society with strong immunity due to high population density, ensuing collapse the native states that may have been able to organize resistance, looting of mass quantities of gold and silver, and mass agricultural slavery. The only difference would have been a slightly greater technological edge for the invaders. Also, there's nothing special about Europeans. If the explorers had been from China via the eastern region, the scenario would likely have played out the same way. Up until modern times, most warfare was either about power, e.g. preventing a rising rival or conquering a falling power, or extraction, where the goal was to remove as much wealth as possible in as short a period of time as feasible. Given human history, extractive warfare against the native population by militarily superior Eurasian invaders would be the expected outcome. So no, I doubt the lack of Columbus's voyage would have done more than set back the timetable a bit, or changed the players. Societies in Eurasia just had too much of a biological (germs from city density), technological, and organizational advantage. That said, what's unique about the Mars colonization idea is that we may have a limited time window in which to try it. Given that our chief sources of energy are non-renewable, we are living in a golden age of cheap production. We haven't so polluted space for Kessler syndrome to lock us in. We even have precociously advanced space technology due to the huge boost from the USA-USSR space race. Right now we're watching our space programs atrophy. There may be a limited amount of time to get a viable off-world colony going. Sure, right now we're talking about an Antarctica-style bunker mission, the Martian equivalent of Apollo. But to get to a true space colony you have to start somewhere.