How effective was the Monroe Doctrine when it was first written? When did it become more effective?

At first, no one took Monroe's doctrine outside the United States seriously.

Explanation:

The Monroe Doctrine is the cornerstone of American foreign policy, setting out certain authorities' views on the Western Hemisphere and the colonies. Given that the position was expressed when the United States did not significantly influence the world, no one took the government's positions seriously. During that period, caricatures were even made at the expense of the United States' foreign policy, which ridiculed the authorities' inability to implement the Monroe Doctrine. Yet as the United States strengthened, the world understood the Monroe Doctrine. That happened especially after the American-Spanish war when the United States crystallized as a world power.