Why do you think so, even in some far future? It's far more likely that Earth governments, having spent hundreds of years propping up such space colonies, would expect to rule them in perpetuity, and have easy means to do so (such as threatening to send nuclear bombardment or even troops - both far easier than actually establishing the colony in the first place). Especially since it seems very likely that colonists would not be allowed in any way to have access to weapons while they are still under Earth governments' control.

Not to mention, the Martian colony would forever be far far more frail to attack than any Earth society, since it has to spend so much of its nature wm resources just to keeping humans alive.

All they would need to do is threaten to stop sending any of a thousand essential commodities that make life tolerable (never mind what makes it possible), and any resistance collapses instantly. Mars colonists would be more directly under the thumb of Earth government than anybody outside of prison, an antarctic base, or navy ship.

I imagine the GP included "in the long run" to refer to a hypothetical future where the colony were truly self-sufficient (so able to produce any good that they want or need).

Not any good they want, maybe, but any good needed for their indefinitely long survival.

Anything they just want badly suffices to enforce control.

Exactly! This is why it eventually would need to become produced locally.

It's not entirely unlike an overseas colony in an inhospitable but not empty place. Start small and dependent, develop the land around you and become autonomous.

Lacking control, how do you bring about diversion of resources to local production?

There's no other point to build a self-sufficient colony on inhospitable and remote Mars. Any scientific missions require much less effort, and afford much higher dependence on supplies from Earth. They don't require a colony, they can make do with an outpost, or 100% robotic presence as now.

Of course the "other" cause may be to make a backup of the Earth civilization and humankind for a case of collapse on Earth, due to global warming, an asteroid impact that hasn't been averted, etc. But this is only possible with true material independence, such that can withstand any blockage or embargo from the Earth's side, else it won't stand the collapse on Earth. The colony may declare allegiance to a particular Earth's government, and inherit the civil norms from the culture(s) which built it, but cannot and must not be ruled from Earth.

Independence != animosity and bitter confrontation. It's more like Canada is independent from the UK, despite some formal allegiance, and the UK is not going to send troops if the Canadian parliament votes in a way that bothers the English monarch.

This is a colossal task, likely not achievable even in this century with the technology we currently have. Stuff like high-temperature atomic engines and other near-sci-fi stuff could alter the equation somehow.

Throughout history, empires have absolutely sent troops when their colonies started clamoring for independence. Now, if Canada wanted to get rid of Charles as head of state and leave the Commonwealth, would the UK send troops? Unlikely, as the cost of the war is very very unlikely to outweigh the benefit of maintaining largely formal control.

But, if Puerto Rico wanted to become an independent nation, do you imagine the USA would let it without trying to quash the "rebellion" with both economic and military might?

> But, if Puerto Rico wanted to become an independent nation, do you imagine the USA would let it without trying to quash the "rebellion" with both economic and military might?

The US did it for the Federated States of Micronesia, Palau, and the Marshall Islands in recent-ish years, why wouldn't they do it for Puerto Rico if they wanted to?

I can't easily find any mentions of the US using military force to compel Palau to submit. It's independent since 1946 or so, and has a comprehensive treaty with the US. Can you please give some keywords or dates of the enforcement actions you allege to?

GP gave Palau, Micronesia, and the Marshall Islands as examples of territories the US allowed to become independent without trying to crush them economically or militarily, so your question seems... misplaced.

Sorry; I misunderstood the example.

My point is that letting a dependent territory go on good terms is a known practice, so thanks for the examples.

Arguably, a Martian colony might be actually more resistant to some forms of attack due to the normally hostile environment & presumably lower population density.

Not to mention any attack coming from Earth and not from some nearby (in ship travel time terms) will be known for months if not years in advance.