Comment by hnbad

Except that the Americas were already inhabited prior to 1490 because they were in fact relatively easily reachable at an earlier point in history and extremely habitable. Mars by contrast is an environment that is actively hostile to life. Even the dust is lethal. And you're so far away from the rest of humanity you can only get resupplies every few years. The Americas had water, soil, edible plants and animals - and practically infinite amounts of breathable air. If you want to go homestead on Mars, dysentery is going to be the least of your worries.