Even though it was not specifically mentioned in the Monroe Doctrine, which country did the Monroe administration also have concerns over because of their interest in the American Northwest?

Monroe administration had concerns over Russia.

The Monroe Doctrine was a policy of the US against European colonialism in the Americas, the doctrine was against the influence of Europe in the affairs of the newly independent Latin American states. The US was also concerned about the northwest coast of America - Alaska toward Oregon - because of Russia's ambitions over there.

Answer:had concerns about Russia