The colonists possessed firearms and metal goods.

They had transatlantic connections.

They were vulnerable enough to need allies.

An agreement with them could strengthen Ousamequin’s position against rivals while giving him a way to monitor the newcomers closely.

The National Museum of the American Indian emphasizes that the 1621 agreement should be understood as a treaty of mutual protection, not simply a friendship pact.

Tisquantum’s role fit this strategy.

He could watch the English because he lived close to them.

He could explain their behavior because he knew their language.

He could help manage communication so misunderstandings did not immediately become war.

In that sense, he was initially useful to Ousamequin because he reduced uncertainty.