How did the reaction of New England Federalists to the War of 1812 demonstrate the volatility of American politics, the divergence of sectional interests, and the fragile nature of the union?
The reaction of the New England Federalists demonstrated all of these things because their reaction was based on their sectional interests and because it, at least to some degree, threatened the unity of the country.
We must remember that, up until at least the time when the Revolutionary War ended, the states saw themselves as separate countries. They created the Articles of Confederation, which tied them together only very loosely under a national government. It was not until the writing of the Constitution in 1787 (ratified in 1789) that the states were united under a strong central government. By the time of the War of 1812, this idea that all the states were part of one united country was still new and not very strong.
Because of this, it is perhaps not surprising that the New England Federalists reacted as they did to the war. The war was something that the Federalists disliked due to their beliefs, but also due to their economic interests. The Federalists were much more supportive of the British form of government than of the French government that arose after the French Revolution. They also represented New England, whose economy depended heavily on trade with England.
This shows how fragile the Union was at this time and how important sectional interests were. The New England Federalist actually met in 1815 at Hartford (the Hartford Convention) to discuss seceding from the Union. They were so different from the rest of the country in terms of their philosophy and their economic interests that they were willing to contemplate breaking away.