There is no single person who can be credited with starting the fight for manifest destiny. It was a product of many factors, including the belief in American exceptionalism, the desire for land and resources, and the westward movement of settlers. However, some key figures who were involved in the fight for manifest destiny include:
* Thomas Jefferson, who believed that the United States had a right to expand its territory to the Pacific Ocean.
* John L. O'Sullivan, a journalist who coined the term "manifest destiny" in 1845.
* James K. Polk, who was president of the United States during the Mexican-American War and who advocated for the annexation of Texas.
* Stephen A. Douglas, who was a senator from Illinois and a strong supporter of the westward expansion of the United States.
These are just a few of the many people who were involved in the fight for manifest destiny. It was a complex and multifaceted movement that had a profound impact on the history of the United States.