Is it ensure, insure, or assure?
An agreement reached by the Pilgrims on the ship the Mayflower in 1620, just before they landed at Plymouth Rock. The Mayflower Compact bound them to live in a civil society according to their own laws. It remained the fundamental law of their colony of Plymouth until the colony was absorbed into Massachusetts in the late seventeenth century.
Note: The Mayflower Compact was the first written constitution in North America.