Handsome Lake was a Seneca leader living at a moment of severe crisis for his nation: the American Revolution and its aftermath had brought major Seneca land losses, displacement and a period of widespread alcoholism and social breakdown within Seneca communities. Handsome Lake himself struggled with alcoholism and serious illness before, in June 1799, reporting the first of a series of visions in which spirit messengers delivered a body of moral and religious teaching.
The teaching that resulted, the Gaiwiio or good message, combined condemnation of alcohol and of witchcraft accusation with calls to preserve ceremonial life, maintain traditional agricultural and social patterns, and hold together as a community, and it absorbed some ethical elements associated with Quaker missionaries then active in Seneca territory alongside its core of Haudenosaunee religious structure. Handsome Lake preached this message actively among Seneca and other Haudenosaunee communities until his death in 1815.
Handsome Lake was the half brother of Cornplanter, a prominent Seneca leader of the same period, and his movement emerged in a Seneca community already navigating the pressures of American expansion, missionary activity, and internal disagreement over how far to accommodate the encroaching United States, context that shaped both the content of his visions and the community's readiness to receive them.
Sources The Ordeal of the Longhouse: The Peoples of the Iroquois League in the Era of European ColonizationDaniel K. Richter with Cornplanter: Chief Warrior of the Allegany SenecasThomas S. Abler