A truly overwhelming operation:
The United States mainland has only three hundred million people, and less than two-thirds can be enslaved by Rocksen. Taking away the rapidly deteriorating elderly, weak, sick, and disabled, the number of people truly controllable is about one hundred million.
Considering industrial raw materials, this land is indeed rich in resources, not only with oil but also a wide variety of minerals...
However, the United States is not the whole world. Whether it comes to labor or raw material reserves, it is not in the same league as the New World Alliance Army.
More importantly, Rocksen is depleting humanity; from top scientists to ordinary workers and farmers, whoever enters Hydra and Rocksen's den waits for a dark future, or rather, no future.