Well it was a war, and settling territory's a traditional part of war. Back then Michigan was a Territory, possession of which depended on who controlled the Forts at the confluence of the Upper Lakes. That was why Tecumseh and the First Nations from far and wide had thrown in their lot with the Brits, to secure that territory to the west as their Homeland, by international treaty. In this case it was the Treaty of Utrecht (after abortive sessions in Moscow and Paris I believe), which betrayed their hopes.Well, no. In 1814, the honours were about even. British invasions were turned back in upstate NY and even the burning of DC was more in the nature of a big raid than a real invasion.
There's nothing in political morality that would commit Britain to investing massive amounts of money and manpower in a military intervention into US territory and internal affairs to protect an erstwhile ally. The territory south of the Lakes was the USA. Britain occupying that territory in order to protect a few thousand Amerindians from the US Army and white American settlers would not have been militarily feasible or legal under international law. The US would ALWAYS have been able to project more military force into the northwest than Britain could and would inevitably have driven the British back out.
I didn't like how the Taliban treated the people of Afghanistan either; but I did not support the Western intervention in that country for the reasons stated above.
My understanding of international law is that it is defined by such treaties, not by the willingness, or ease of a nation to project its power abroad. 'Abroad' was only just across the Lakes, and as you say, neither nation was able to accomplish 'projection of power'. Since it was the American purpose, thus the conclusion they lost, along with Tecumseh. I'm sure it's my misunderstanding when I read you as suggesting the US would have broken such a treaty—with the ink hardly dry—and forced Britain to renew hostilities in the NorthWest had the provisions favoured the Indians. But they did not, leaving the West to be taken up by those settlers once the inhabitants had been killed or driven off. A better deal than conquering Quebec, Upper Canada or Rupert's Land.
Of course the record with regard to subsequent treaties between those white American 'settlers' and the First Nations who then had only American law to depend on was savage and sad.