How might Europe have responded to the Monroe Doctrine if the US was not friends with Great Britain?

Answer 1

Definition of Monroe Doctrine
Just to be clear, the Monroe Doctrine was a statement made by US President James Monroe in 1823 that effectively stated several things: (1) that new attempts by European nations to create new colonies or re-colonize newly independent states in the New World would be viewed negatively by the US, (2) that the US would intervene in any such conflict, and (3) that the European nations were free to maintain current colonies and internal affairs without the US meddling with those.

Most European countries laughed at the US for proposing this because the US had no means of effectively fighting against them. It was Britain's support for the Monroe Doctrine that made the Doctrine more-or-less followed.

Concerning Friendship
The cordial relations between the US and UK in 1823 had no bearing on Europe's response to the Monroe Doctrine. The US and UK would only truly become "friends" in the later 19th century after the US Civil War. However, the Monroe Doctrine is often see as a precursor to the "US-UK Special-Relationship" which was well-established in the 20th and 21st centuries.

Since "friendship" did not really exist between the US and UK in 1823, the presence or lack of friendship was IRRELEVANT in determining Europe's leaders' responses to the Monroe Doctrine.

Actual Reason for Success
What Britain did that made the Monroe Doctrine successful was their Foreign Secretary George Canning's statements that the British Navy would enforce and defend the Americas from European intervention along the lines stated in the Monroe Doctrine. Because Britain was the most powerful country in the world, as opposed to the US, which was relatively weak, the British approval was critical and lead to the Europeans acquiescing to the terms of the Monroe Doctrine.

If Britain had not supported the Monroe Doctrine (or actively opposed it), it would have been a worthless speech. European Powers that had recently lost colonies in the New World, like Spain and Portugal, would likely have attempted to reclaim those territories. Other European Powers would try to conquer recently independent countries, like France actually did when Napoleon III decided to invade Mexico in 1861 because the US Civil War prevented direct US intervention to protect Mexico. Others would want to extend their current colonies, such as Russia had tried in the Ukase in 1821.

Answer 2

I think Europe might have responded to the Monroe Doctrine if the U.S was not friend with Great Britain by them having to regain their trust for each other and become friends again.