Results of that nasty little war

Of 1812, that is.

Nasty or not, it was important.

Before the war, the geographical and legal boundaries of the Anglophone world were ambiguous; lots of people were more concerned about the radical Democratic-Republican or conservative Tory or Federalist next door than they were about people who lived on the other side of the ill-defined border. Not to mention all those radical Irishmen who could be anywhere, as indeed could Irish conservatives.  How different were American farmers in New York State from "Late Loyalists" in Upper Canada (i.e. Americans who had moved north to buy cheap land)?  Not much, though some were more radical than others, or perceived as such.  Geography did not determine this.

But after the war, the border (the UC-USA border) meant a lot.  On  the other side, whichever side you  lived, were people who had burned your houses and wrecked your farms and maybe unleashed scary Indians on you.  They were now The Enemy in a way that they had not been before.  Migration was not welcome; the policy in Upper Canada became one of recruiting settlers direct from Britain.
 
I also get from Alan Taylor the  notion that Britain came very close to winning the war outright.  The treaty of Ghent of 1814 gave the USA very little of what it had fought for, and with Napoleon out of the way, Britain could have crushed the broke, divided States like so many bugs, even while observing the treaty.  Instead, the imperial government took a rather minimalist view of  its role in North America. In particular the traditional alliance with the Indians south of the lakes was abandoned.

Why?  The empire had been fighting a world war for a long time and was TIRED. And the Battle of New Orleans made the point that hegemony in America would probably not be cheap.