The most prominent episode in Mason's lifelong career of public service was his overall command as captain of the Colonial forces in the Pequot War in 1637. This was the first declared and sustained conflict in Southern New England, a complex and risky campaign. The large and powerful Pequot Tribe had subjugated other local tribes, killed numerous Colonial settlers and destroyed vital corn crops. The Massachusetts Bay Colony eventually declared war with them, and reluctantly the infant Connecticut Colony was quickly drawn into the conflict.