"The root cause was mercantile, with that of impressment of US citizens for service in the British navy as a secondary cause."

Those were reasons aired for public consumption, the excuses given. The US at the time could do absolutely nothing to alter the restrictions placed on their trade or on the right of search and impressment exercised by the Royal Navy of that time. The United States of America simply did not have the naval power to challenge Britain, or alter the status quo.

There was only one thing that the United States of America could gain by going to war with Britain in 1812, a Britain engaged in the largest war Europe had ever experienced, and that was land. That and that alone was America's war aim, it had absolutely nothing to do with trade or impressment, they were the lies d'jour sold to the US Congress of 1812, they bought them and they lost. Canada stood, the US Army of the day being beaten off by a combination of Canadian Militia Regiments and Native Americans. The sacking of Washington and the burning of the White House later in the war were the result of a raid, the British having no desire whatsoever to embroil herself in yet another war, that would gain her nothing. The colonies that became the United States of America had been written off by Great Britain as being not worth the effort to retain in the revolutionary war of 1776. Britain still felt the same 36 years later.