In order for mankind to establish civilization on other planets, there are multiple issues we must deal with first.
Given the spectacularly large distances between objects in space, we must work out a method of moving quickly enough from our planet to another potential host planet within our natural life spans, or extend those life spans to suit the journey, as would be the case using cryogenic suspended animation.
At great enough distances, man cannot communicate effectively with earth. At a light-year away, they would take many, many years to reach our home planet. Light pulses would diminish in signal strength over distance, and require a clear shot to Earth or a relay satellite to be practical.
3. Life Support
This encompasses sustaining life both on the trip, and on the newly discovered planet. The cargo demand would be massive for an actual colonization effort, if only to sustain the basic necessities for life. Also, to ensure an adequate gene pool, there would need to be many colonists. Oxygen, pure water, protection from the elements; all would require a large amount of equipment, far greater than any space station.
These three obstacles alone are enough to doom any colonization effort, and that's disregarding all the other dangers of space travel. In order to be a meaningful colony, the planet will have to be naturally inhabitable. Shelters large enough to house a significant population against an utterly hostile planet is simply not practical. This means the nearest POSSIBLE inhabitable planet is near Alpha Centauri, still quite a few light years away.
All in all, the possibilities are bleak. Physics will only allow technology to advance so far.