It was The Christian Commonwealth by John Eliot.
Eliot was a theologian, Bible translator, and political writer. He translated the Bible into Algonquin, or Massachusetts, in 1661 (that's right, I just wrote 1661).
He is most known for his efforts to create a new civil order among the Indians he served as a missionary. He emphasized the need to protect indigenous culture while at the same time organizing the Indians into towns focused on living a Christian life both privately and publicly. He was known for leading the "Praying Indians"
Ultimately, his vision of a Christian society among the Indians would be destroyed by English settlers who didn't like to see the advancements in Indian culture that missionaries were introducing (literacy, health reform, and a respect of basic human rights) and were threatened by the Indians' alliance with France.
Wikipedia notes that Eliot's book was the first book to be banned by an American government (not the US government as it didn't yet exist). He proposed a system of government based on Exodus 18 which proposed dethroning the King.
That can get you into trouble.
You can download the whole book here.
Sources: Evangelical Dictionary of World Missions, ed. by Moreau, The Christian Commonwealth by Eliot, and Wikipedia.