Answer :
Final answer:
a. John O'Sullivan coined the term 'manifest destiny' in 1845, encapsulating the idea of divinely sanctioned American expansionism.
Explanation:
The individual who described the spirit of American expansionism in 1845 with the words "our manifest destiny . . . to overspread the continent allotted by Providence for the free development of our yearly multiplying millions" was a. John O'Sullivan.
O'Sullivan, a magazine editor, introduced the term Manifest Destiny which became a rallying cry for westward expansion, embodying the belief that Americans were divinely destined to expand their democracy and culture across the continent.
While politicians like Senator Thomas Hart Benton were leading proponents of the ideology, it was O'Sullivan's articulation that cemented the concept in the American lexicon.
