Answer:
The major obstacle to the doctrine of Manifest Destiny was the existence of other sovereign nations on the continent.
Indeed, the doctrine of Manifest Destiny established that the United States had the mission of extending from the Atlantic Ocean to the Pacific Ocean, expanding civilization in the Americas.
But the truth is that the United States had certain well-defined geographical limitations: the British colonies to the north, which would eventually become Canada today; and the French and Spanish colonies to the west and south, part of today Mexico and part acquired by the United States through the Louisiana Purchase, the acquisition of Florida and the Mexican-American War, in addition to the various acquisitions of native territories.
Once the territory of the contiguous states was consolidated, the nation met with two nations also territorially and sovereignly consolidated to the north and south of the country. Therefore, from this moment the continental expansion found its final limit, and subsequent acquisitions (Alaska, Hawaii, Puerto Rico, etc.) had an overseas character.
