James Fenimore Cooper (September 15, 1789 - September 14, 1851) was a prolific and popular American writer of the first half of the 19th century. His historical romances draw a picture of frontier and American Indian life in the early American days which created a unique form of American literature. He lived most of his life in Cooperstown, New York, which was founded by his father William on property that he owned. Cooper was a lifelong member of the Episcopal Church and contributed generously to it.

James Fenimore Cooper was born in Burlington, New Jersey in 1789 to William Cooper and Elizabeth (Fenimore) Cooper, the eleventh of 12 children, most of whom died during infancy or childhood. He was descended from James Cooper of Stratford-upon-Avon, Warwickshire, England, who immigrated to the American colonies in 1679.  Shortly after James' first birthday, his family moved to Cooperstown, New York, a community founded by his father on a large piece of land which he had bought for development. Later, his father was elected to the United States Congress as a representative from Otsego County. Their town was in a central area of New York that had previously been occupied by the Iroquois, who had allied themselves with the British during the Revolutionary War and were forced to cede the territory after British defeat. The State of New York opened the land for sale and development after the war, and Cooper's father purchased several thousand acres in upstate along the headwaters of the Susquehanna River. By 1788, William Cooper had selected and surveyed the site where Cooperstown would be established. He erected a home on the shore of Otsego lake and moved his family there in the autumn of 1790. He soon began construction of the mansion that became known as Otsego Hall, completed in 1799 when James was ten.  Cooper was enrolled at Yale University at age 13, but he incited a dangerous prank which involved blowing up another student's door -- after having already locked a donkey in a recitation room. He was expelled in his third year without completing his degree, so he obtained work in 1806 as a sailor and joined the crew of a merchant vessel at age 17. By 1811, he obtained the rank of midshipman in the fledgling United States Navy, conferred upon him on an officer's warrant signed by Thomas Jefferson.  At 20, Cooper inherited a fortune from his father. He married Susan Augusta de Lancey at Mamaroneck, Westchester County, New York on January 1, 1811 at age 21. She was from a wealthy family who remained loyal to Great Britain during the Revolution. The Coopers had seven children, five of whom lived to adulthood. Their daughter Susan Fenimore Cooper was a writer on nature, female suffrage, and other topics. She and her father often edited each other's work. Among his descendants was Paul Fenimore Cooper (1899-1970), who also became a writer. Answer this question using a quote from the following article:

Who did they side with
who had allied themselves with the British during the Revolutionary War and were forced to cede the territory after British defeat.