As the sachem of the Wampanoags, the decision of how to respond to the newcomers was Massasoit's to make. Yet his decision was influenced by the events around him. Shortly before the Pilgrims arrived, a terrible plague, probably introduced by English fishermen, nearly wiped out the people of the Wampanoag confederacy. This left them in danger of destruction from the Narragansetts, their enemies to the west. When the Pilgrims arrived, Massasoit was uncertain of how to respond, and it is true that the Patuxent/English ambassador Squanto (who had lived in England for a time as a slave, and spoke good English) urged the sachem to pursue peaceable relations with the newcomers.
But the main reason for Massasoit's approach seems to have been the strategic situation facing the Wampanoags. They needed allies, and the Pilgrims seemed an ideal choice to alter the balance of power in the region. Additionally, Massasoit became persuaded that the Pilgrims, who had arrived with women and children, did not intend to make war on them. The Wampanoags seemed the more imminent, and the more dire threat, and so Massasoit heeded Squanto's advice, a decision he, and his son Metacom (King Phillip) would come to regret.