In the mid-1800s, travelers faced the greatest risk of attack by native american groups on the

The Santa Fe Trail.

Explanation:

The Santa Fe Trail was a 19th-century transportation route through central North America that linked Franklin, Missouri with Santa Fe, New Mexico. The route of the Santa Fe trailed crossed the territory of the Comanches, the north-western corner of Comancheria which are a Native American nation. The mid-1800s, travelers faced a high risk of attack by Apache and Comanche groups.

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nothing certain is known about what happened, but it seems that the country declined gradually, perhaps due to bad government, or, more likely, due to a series of bad harvests, which resulted in widespread and recurrent famine.