George Henry Haskell in the War of 1812
The thing I didn't know about the War of 1812 is that it mainly happened in 1814, at least in New England, when British fleets menaced the Maine coast and occupied territory east of the Penobscot. This explains why George Haskell was not with the Massachusetts militia in 1812, when he was otherwise engaged in burying one wife and marrying another.
There was a Captain Haskell who played a role in the events of September 1814, when a raiding party of 70 redcoats attacked the small garrison at Sandy Bay, near Gloucester. However, this was a Benjamin Haskell from a Gloucester branch of the family. (The Haskell or Haskall family was prominent in Plymouth and throughout Massachusetts in the colonial and revolutionary periods.)
A better bet for the service record of George Henry Haskell is around the same dates but serving among militia units defending the city of Portland, Maine. Reinforcements sent to Portland's harbor forts deterred the feared British attack on the city, which never came.
Ancestry suggests that the George Haskell who served in Portland (in the Company of Joseph Valentine, Regiment of Lt. Col. Josiah Hobbs) may be our man. However, this George Haskell was listed with the rank of private and is in the same company with an apparent brother Nathaniel, yet our George had no brother by that name.
I'll look for a more convincing explanation for Haskell's later honorific use of the title of Captain.
The signing of the Treaty of Ghent in December 1814 ended the war with the return of conquered territory, including in eastern Maine. Five years later, Maine separated from Massachusetts and was admitted as a sovereign state of the United States.
After his service in Portland, George Haskell returned to his family in Middlebury, Vermont, where he remained until establishing a homestead in Chautauqua County, New York.