Final answer:
The term Manifest Destiny was first used by John L. O'Sullivan in 1845, signifying a divinely supported mission for American territorial expansion, which heavily influenced the politics and geography of the mid-19th century United States. The correct answer is option d.
Step-by-step explanation:
The earliest known use of the term Manifest Destiny was by John L. O'Sullivan. The concept of Manifest Destiny found its roots in the long-standing traditions of territorial expansion and was coined by magazine editor O'Sullivan in 1845, when he wrote in the United States Magazine and Democratic Review about America's divine encouragement for territorial expansion. This concept justified the westward expansion movement in the United States during the 1840s, asserting that the American expansion was inevitable, just, and divinely foreordained. A critical phase of this expansion was the addition of Texas and Oregon to the Union, leading to the war with Mexico and the acquisition of territories including California.