The president most responsible for obtaining the lands of California, Oregon, and New Mexico for the United States was James K. Polk. Option C is correct.
James Knox Polk was the 11th president of the United States. Prior to his presidency, he was speaker of the House of Representatives and governor of Tennessee. He belonged to the Democratic Party and was an advocate of Jacksonian democracy. During Polk's presidency, the United States expanded significantly with the annexation of the Republic of Texas, the Oregon Territory, and the Mexican Cession following the American victory in the Mexican–American War.
