Comment by valarauca1

Sadly the pathogen make up of the Americas made safe exploration an impossibility until man-kind had achieved 20th century medical technology.

Even then it would have extremely struggled to handle 30+ million new cases of Small Pox, TB, Bubonic Plague, etc.

Luckily as far as modern technology can show we're extremely certain Mars has no life we'll accidentally genocide while exploring/terraforming.