Mars is such an interesting case study. I watched a TED talk given by Stephen Petranek called, "how we'll live on Mars", It's a great watch, I think it is only a matter of time before humans conquer the red planet. Once the early explorers land it will be very difficult, but they will have to rebuild the atmosphere and slowly construct a civilization. What will make this happen is the ingenious technology coming from companies like Space X, where they are able to reuse rockets, slashing costs tremendously. If I had to put a time frame on it, I would say there will be earth born humans inhabiting and possibly procreating on the red planet by 2030.
heres the link to the video, he also has a short book on the same subject.
https://www.ted.com/talks/stephen_petranek_your_kids_might_live_on_mars_here_s_how_they_ll_survive