Battle for Terra, about a spacefaring colony of surviving humans fleeing
our Sol system after they pretty much wrecked the place and coming
upon a planet inhabited by nice aliens who live in harmony with their
nature.

Guess what happens next?

To add some extra intellectual meat here, what will we do some day if
we do find an Earthlike world out there in the galaxy and we still have
not changed all that much except for having shinier toys?

Do we go and colonize an Earth type world just because it is there?
Such a place is bound to have inhabitants by its very nature, and even
if they are not intelligent (now there's a sticky wicket), do we have the
right to push them out of the way, or use them to make living on that
new world easier?

The exoplanet searches are all trying to find their Holy Grail, the Earth
sized (and presumably Earth like) world. The understated point (and
sometimes not so understated point) after hoping it has life and therefore
proving that terrestrial organisms are not some kind of cosmic fluke is
to see if it might make a nice place for our children to live on some day.

I often wonder if, since the whole point of life on this planet and
presumably elsewhere is to find new territory as the species and
numbers grow, Heinlein's Starship Troopers (especially the 1997 film
version) is the reality of what is happening out there and will happen
with us some day if we enter the fray - or if the fray comes to us.

Do intelligent species form some kind of Federation/United Planets in
order to get along, or is it every being for itself, with the winner getting
the whole galaxy?