Following his father's death, John Underhill and his siblings lived with their mother and a group of Puritan exiles in the Netherlands.

He also married a Dutch girl, Helena (Heylken) de Hooch on 12 December 1628 in the Kloosterkerk, The Hague, Holland.

Using the Narragansett killing of a Plymouth Colony-exile and the mistaken killing of an English pirate by the Pequot people as a pretext, the English colonists decided to go to war against the Pequots who controlled the regional wampum trade and coastal lands desired by the Puritans.

Joining with Mohegan allies and Connecticut militia under Captain John Mason, they attacked the fortified Pequot village near modern Mystic.

Still finding no gainful employment in Boston, following the baptism of his son John III in April 1642, he leased a tobacco plantation in Flatlands, Long Island, in New Netherland.

Following Indian raids in 1643, he was hired by the New Netherland Board of Eight Selectmen to attack Lenape settlements.

In February 1644, working for the Dutch, Underhill slaughtered an estimated 500 to 700 Lenape, thought to be of the Siwanoy and Wechquaesgeek bands of the Wappinger Confederacy.

His plot of land at the southern end of the island was later developed as the site of Trinity Church in Manhattan.

Just as many of his descendants would enumerate George III's wrongdoings, so he described Stuyvesant's; he had, for example, imposed magistrates on the people of Flushing "without election or voting."

In conclusion, Underhill declared, "This great autocracy and tyranny is too grievous for any brave Englishman and good Christian any longer to tolerate Accept and submit ye, then, to the Parliament of England."

Upon hearing of Dutch plans to ally with some tribes to attack the English settlements, Underhill brought word of this to the colonies in Connecticut.

Fearing an attack by troops led by Underhill, Stuyvesant ordered that a high stockade and a small breastwork be constructed across the northern border of New Amsterdam.

This place was on the eastern edge of New Netherland and far enough out of reach of Massachusetts Bay and other colonies to give Underhill a respite from war, conflict, and religious intolerance.

Underhill eventually retired to a large estate (Kenilworth or Killingworth) at Oyster Bay on Long Island.

Underhill agreed on passage of a law that settlers could make no land purchases from the Lenape in the future without the government's consent.

[8] The following year as Chief Advisor to the Matinecock Indians (a Lenape band named by the English for their location), Underhill presented a petition to the Council of Assizes in 1666.

The events contributed to the principles codified a century later in the First Amendment in the Bill of Rights, granting religious and political freedom to all citizens.

Son Nathaniel Underhill settled in Westchester County, New York, where he became a prominent citizen and the progenitor of a large number of descendants.

An excerpt of a letter from Captain Underhill to Hanserd Knollys appears in The Algerine Captive by Royall Tyler published in 1970 by Rowman & Littlefield.

He served in the army of the Prince of Orange before coming to New England and was married to a Dutch woman.

Ultimately he rejected these affiliations with the Netherlands and strongly asserted his patriotic commitment to England and English claims to North America.