Maybe the best Martian policy would be to prevent anyone from colonizing Mars, rather than to colonize it first.
Let’s assume for a moment that Mars really can be developed into a self-sufficient Earth 2.0. A big if, of course.
But if true, then see: The New World.
Settlers always have high asabiya, thanks to the challenges they face, and homogeneous interests relative to those who remain in the Old World, with its historic divisions. The Old World always thinks it can control the new, otherwise it wouldn’t foolishly bankroll settlers. But the new is far, far away. It is protected by distance. It is bigger than the territory of any one mother country.
And because it is united—or will become united, because, again, regardless of the origin of the settlers, their interests are always more in common with each other than with those of their mother countries—it can exploit this bounty at scales that no one mother country can ever hope to match.
So, eventually, the new will know its own power and come to dominate the old.
It has, after all, happened before.
And even if we don’t think Mars might be viable, or we think it might be more likely to make a Cuba than a U.S.A., why risk it?
Indeed, colonizing activity by a dominant country is always a self-inflicted wound. Colonization necessarily dilutes the dominant country’s power, because any new territories dilute the power of the earth entire. If I’m two thirds of one and I add one, now I’m one third. The only reason to colonize is to preclude others from doing so; it’s a race to the bottom.
But you can also try to enforce a rule against racing.
And if you were wondering why, in the 15th century, it was the Spaniards who went off looking for new worlds, and not the great powers of the day, not the Ottomans or the Chinese, you have your answer.