Which of the sentences below best expresses the essential information in the highlighted s
A．At the time, the U.S. was struggling against many other nations to gain control of western lands.
B．The American government encouraged all people, regardless of their background, to settle in western regions.
C．Mexico, England, and the Native Americans all fought with America for the rights to the western territories.
D．U.S. authorities supported westward migration as it kept other peoples from taking over the land there.