Perhaps I"m being idealistic about the motivations of our early political leaders but I do think that the primary reason behind the war of 1812 were patriotism and honor. The way Madison justified the war, in his war message 1 June 1812, was by highlighting the British aggression on the seas; primarily impressments, British cruisers hovering near ports, blockades and the orders-in-council. The Americans also believed the Brits guilty of inciting Indian uprisings.
The United States attempted to avoid engaging in this European conflict through peaceable negotiations and economic coercion. But they could not ignore obvious British disrespect for their sovereignty. The British impressed thousands of sailors from American ships and obviously did think American retaliation to be a real threat. "No nation mindful of its diplomatic fences would have kidnapped 3,800 neutral aliens of one nationality."(Smelser 224).
England forced the United States to choose between submission and war. They treated American grievances like internal problems, again not respecting the sovereignty they had fought to earn. The decision to declare war was not made lightly. Madison was not a war monger like Napoleon, but honor compelled him to act, as well as the desire to not see America reduced to a British protectorate. Madison believed he was protecting what he called, "the last and fairest experiment in favor of the rights of human nature.", what we might call the American way of life.
The American decision to go to war with England but not France is further evidence that honor and patriotism were the guiding reasons behind entering the war. It would have foolish to enter a war with the whole of Europe, which engaging both countries would surely do, but there were ample grievances against both (Coles). Henry Clay justified the decision to proceed with war against Britain but not France by saying, "As to France we have no complaint but of the past.