The Mayflower Compact, signed in 1620, was the first governing document of Plymouth County, written by separatist Congregationalists. The original document has been lost, but three versions still exist. The document contained heavy themes of Christianity, democracy, liberty and religious freedom.
The Mayflower was originally headed for the already established Colony of Virginia but did not make it, and instead the pilgrims had to anchor down and live in what is now Cape Cod, MA. Because they were in new land with no established rulers, they took it upon themselves to establish their own government so that no one from outside could rule them. This is why the document, based on a majoritarian model (although women and children could not vote), contains many themes of liberty and democracy.
"Having undertaken, for the Glory of God, and advancements of the Christian faith and honor of our King and Country, a voyage to plant the first colony in the Northern parts of Virginia, do by these presents, solemnly and mutually, in the presence of God, and one another, covenant and combine ourselves together into a civil body politic; for our better ordering, and preservation and furtherance of the ends aforesaid; and by virtue hereof to enact, constitute, and frame, such just and equal laws, ordinances, acts, constitutions, and offices, from time to time, as shall be thought most meet and convenient for the general good of the colony; unto which we promise all due submission and obedience."
The document was essentially a social contract.