I would say it was when the Pequot tribe murdered the English trader (John Stone) and his crew....but it goes deeper then that. The Pequot people pretty much controlled all trade in the region. They extended their political and economic ties through coercion and warfare. This caused major tension between the tribes of the area. With the arrival of English traders, the balance shifted which resulted in conflict and intense competition for power. So it wasn't just the death of the English trader...but also decades of tension between the native tribes further stressed by the arrival of the Dutch and English.
