In what year did the US acquire 181 million acres through the Oregon Annexation?

The correct answer is 1846, as this year marks the signing of the Oregon Treaty between the United States and Great Britain. The treaty resulted in the U.S. gaining control over the Oregon Territory, which encompasses a vast area that includes present-day Oregon, Washington, and parts of Idaho, Montana, and Wyoming. The acquisition of approximately 181 million acres through this treaty was significant in expanding U.S. territory westward, aligning with the concept of Manifest Destiny, which was the belief that the U.S. was destined to expand across the North American continent.

The other years referenced in the options are associated with different historical events and territorial changes. For example, 1854 is associated with the Kansas-Nebraska Act, which organized territories but did not pertain to the Oregon Annexation. The year 1867 is significant for the acquisition of Alaska from Russia, and 1820 relates to the Missouri Compromise, which dealt with the expansion of slavery in new territories rather than territorial acquisition like the Oregon Treaty. Thus, 1846 is the specific year directly connected to the Oregon Annexation and its substantial territorial gain for the United States.