Why Europe did not collectively challenge the Monroe Doctrine

What would have happened if the European powers collectively rejected the Monroe Doctrine over Cuba?

A collective challenge was possible in theory, but Britain repeatedly refused to join one; without British backing, Spain could not assemble a united European front.

European cooperation against the Monroe Doctrine depended on Britain's willingness to participate. Other powers could contemplate a joint warning, but Britain repeatedly decided that challenging Washington was not in its interest. Spain sought a collective European declaration supporting its position in Cuba, and London declined to sign. With the leading naval power outside the coalition, the proposed diplomatic front went nowhere.