門羅對歐洲國家的政策宣言並未即時形成門羅主義，直到約三十年後才有門羅主義的出現；1823年，美國並沒有足夠的實力執行門羅的宣言，在美國之外的地方，很少人知道這個政策的內容。

在十九世紀早期，美國逐漸成為世界強權，門羅主義也成為美國外交政策的基礎，西奧多羅斯福總統於1904年在門羅主義中加入「羅斯福推論」（Roosevelt Corollary），內容言明美國擁有介入拉丁美洲國家事務的專屬權，包含拉丁美洲國家蓄意的不當行為或是拒絕償付國際債務等情事。

Monroe's declaration of policy toward Europe did not become known as the Monroe Doctrine until about 30 years after it was proclaimed. In 1823, the U.S. was not powerful enough to enforce Monroe's proclamation. Outside the United States, the "doctrine" went mostly unnoticed.

In the early 1900s, the U.S. emerged as a world power and the Monroe Doctrine became the foundation of U.S. foreign policy. President Theodore Roosevelt added the "Roosevelt Corollary" to the Monroe Doctrine in 1904, which said the U.S. had the exclusive right to intervene in the affairs of Latin American countries that were actively involved in deliberate misconduct or that refused to pay their international debts.

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