Answer:
western lands
Step-by-step explanation:
Most of the territory the United States acquired in the nineteenth century was located in "Western Lands."
Firstly, it was through the Louisiana purchase in 1803 from France, which cover the western half of the Mississippi, then span across the present state of Arkansas, Missouri, Iowa, Oklahoma, Kansas, and Nebraska; and a big part of North Dakota, South Dakota, etc.
Also, following a war with Mexico between 1846 to 1848, the United States gained further lands in the western territory which span from Kansas to California.