What policy did Congress adopt that was proposed by John J. Crittenden of Kentucky? What was required of northern military commanders?

Crittenden Compromise

Explanation:

made up of six proposed constitutional amendments and four proposed Congressional resolutions that he was hpoing would appease Southern states and help the nation avoid a civil war. 

support by the South and not by the North, it was a failure.

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explanation:

the answer to your question is a. the salt plains

in 1811, he led an expedition, known as the george c. sibley expedition, to improve relations with the pawnee and kansa tribes, and also to locate the rumored jefferson's salt mountain