Why would a sachem be concerned about the defection of a small settlement

Because that would weaken the small settlement even more.

Explanation:

Sachem is the term used by Northeastern Native American tribes to refer to its supreme leader. The Sachem had to lead the tribe, solve the problems and protect those who were subordinate to it. The Sachems were very concerned about the desertion in small villages, because these villages were already weakened by their small size and the desertion would weaken much more because it could lose some warrior to the enemy.

The deserter would know the tactics and weaknesses of the village, so if defections occurred, more serious problems could arise.

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