The exact date, location and reasons behind the first Thanksgiving celebration are a source of contention. It is generally accepted that the origins of our modern day celebration in the United States results from the 1621 harvest celebrations in Plymouth, Massachusetts, when the Wampoang Native Americans saved the pilgrims from starvation. The date for observance was not fixed until 1941, when Franklin Roosevelt signed a bill into law with Congress.
Historian Jeremy Bangs, the director of the Leiden American Pilgrim's Museum, believes that the annual observance of Thanksgiving may have been influenced by a tradition that commenced following the siege of Leiden (Netherlands) by the Spaniards in 1574. Thanksgiving Day is also observed in Leiden.