I think you're badly overstating the influence of the secessionist movement at the Hartford Convention. But regardless, it's interesting to note that at least one prominent Richmond looked at the extremist minority's proposal for secession and called on the federal government to take whatever steps were necessary to "save the Union".
In the War of 1812, the USA was invaded by Great Britain which, apparently, had not gotten over its loss of "the colonies" and wanted a re-run of the previous war (and got a re-run of the result), sacked our Capitol, burned the White House, but had to agree to peace (Treaty of Ghent signed by the Brits but not yet ratified by our Congress) even before learning of Andrew Jackson's massacre of the Brit Army under General Edward Pakenham (Wellington's brother-in-law) at the Battle of New Orleans. Pakenham's grape shot-riddled corpse stuffed into a whiskey barrel and preserved by being packed in the remaining whiskey, had not yet arrived at the home of the widow Pakenham.