Why did imperialists cite economic opportunities, racial theories,
competition with European empires, and the perception in the 1890s that
the Western frontier was "closed" to argue that Americans were destined
to expand their culture and institutions to peoples around the globe? *

Imperialists wanted the US to expand its territory for greater power and influence.

Explanation:

The time of 1890s was an important period in Us because here were two factions that were discussing how US would approach the world in the future.

The Anti imperialists wanted the country to rely on its old tradition of self determinism and isolation to develop the country to greater heights and saw that there would only be conflict like the European nations if they were to expand.

The Imperialists saw it differently, they knew that the country needed more resources and to make sure that it was possible they needed more ground covered and they were also alive to the fact that European influence of expanding their culture and institution had brought the, great profits and power.

imma say false because i dont know anything about this.

the commander in chief