Page "John Burgoyne" Paragraph 21

Rather than an outright unconditional surrender, Burgoyne had agreed to a Convention that involved his men surrendering their weapons, and returning to Europe with a pledge not to return to North America.

Burgoyne had been most insistent on this point, even suggesting he would try to fight his way back to Quebec if it was not agreed.

Soon afterwards the Continental Congress, urged by George Washington, repudiated the treaty and imprisoned the remnants of the army in Massachusetts and Virginia, where they were sometimes maltreated.

This was widely seen as revenge for the poor British treatment of Continental prisoners.