What if the green men there neither allow migration nor have oil?
Because oil is really going to be a concern when we can launch ourselves 1,400 lightyears.
Generally speaking, by time we have the capability to traverse interstellar space, it will be just as easy to build deep space colonies as it will to search out planets that we could colonize. The time and energy invested in constructing a known quantity is less than the time and energy spent investigating entirely unknown quantities.
That won't stop us from looking to colonize other worlds - but the reality is that anything that is inhabited by a sentient species is not worth even the risk of announcing our presence to (particularly if they have comparable space travel capabilities). If a planet is inhabited - just move on and continue building colonies.
I imagine there will still be wars in space - but they will most likely be 'civil wars' fought amongst a species rather than two species fighting each other. Humans will have plenty of reason to fight each other over territory we occupy - claims to asteroid mining, specific holdings on a colony, etc. For a species that has no vested interest in a territory they happen across and find to be occupied - it would be quite the rare instance for there to be a resource worth going against an established system's industry to acquire.
While advancement is difficult to predict - I expect we will be performing experiments on 'jump drives' within the next 100 years. IE - a device that allows a ship to simply shift into a position many lightyears away (though I imagine the first experiments will be on the order of a few thousand kilometers).
Of course, people 30 years ago were predicting flying cars and other such things by now - so it's kind of hard to predict which direction things will go.
