How did William H. Seward aid US expansion?

William H. Seward significantly aided U.S. expansion through his role as Secretary of State under Presidents Lincoln and Johnson. He is best known for orchestrating the purchase of Alaska from Russia in 1867, a move that expanded U.S. territory and resources. Seward also promoted the idea of American influence in Central America and the Pacific, advocating for the construction of a transcontinental railroad and supporting various diplomatic efforts to extend U.S. borders and influence. His vision laid the groundwork for the later continental expansion of the United States.