The United States bought Alaska in 1867 to

keep Russia from expanding toward the US mainland.
stop other countries from taking over the territory.
control the territory’s abundance of resources.
open a critical trade route with the Far East.

Hello again the correct answer to this A. keep Russia from expanding toward the US mainland.

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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