What event led monroe to issue his warning statement?

On December 2, 1823, President James Monroe used his annual message to Congress for a bold assertion: ‘The American continents ... are henceforth not to be considered as subjects for future colonization by any European powers.’ Along with such other statements as George Washington’s Farewell Address and John Hay’s Open Door notes regarding China, this ‘Monroe Doctrine’ became a cornerstone of American foreign policy. Secretary of State John Quincy Adams had played the most important role in developing the wording of the declaration, and he also influenced the doctrine’s overall shape.

The chance of increased European involvement in the Americas President Monroe. There was also concerns about Russia's intentions for controlling land in the northwest.