There's always more to be said, but in the meantime you can check this thread by u/enygma9753 for an explanation about the complicated relationship between European settlers and the native peoples, and British commitments to the natives re: safeguarding "Indian territory" west of the Appalachians in the aftermath of the 1759 conquest of Quebec and the fall of New France. These were enshrined in the 1763 Royal Proclamation which set the original limits of white settlement after the Seven Years War.

Britain was short on manpower in the Canadas in 1812, with its resources devoted to fighting Napoleon. It needed to secure native alliances to bolster its ranks against American invasion and also saw strategic value in having native territory as a buffer zone to separate its Canadian colonies and the US. Tecumseh, leader of the pan-native alliance, sought to create a unified native homeland and welcomed the chance to fight for one on the British side.

The native cause was betrayed during the peace negotiations at Ghent, when Britain reneged on its promises to the natives, thus allowing American westward expansion to continue without restrictions.