except they didn't truly conquer those places, they just colonized the populations (and sustainabloid life patterns) already present...
There would have been indications in wave pattern. And they knew how to read these, as well as meteorological hints and knowledge of tides.
Nevertheless, in the context of this discussion, landing up on an inhabited island thousands of kilometres from here is a huge shot in the dark, and most hopeful colonists would have missed.
But on Mars, you don't have proper air and you don't have wild life for food. And you cannot easily leave for other better places.
Once the location is established, regular trade becomes much more feasible.
Good point. It would make sense to send robots in advance to manufacture huge stockpiles of air and food. Which is of course beyond present technology.