The North American continent has a relatively small population with ample agricultural land to grow food, forests to provide shelter, oil, gas and coal to provide energy, fiber to make clothing, and resources to provide for our defense.
We’ll be fine so long as we don’t foolishly waste everything trying to dominate the rest of the world.
An unstable world is a serious threat to the United States.
The oceans are no longer the defense they used to be. A hostile Mexico and Canada become serious possibilities. Religious fanatics and non-state actors can inflict serious harm - they thrive in an unstable world.
Relying solely on domestic raw materials nets you a mid-19th-century economy. Even railroads disappear for want of those elements critical for alloy steels to make the rails out of. Without them, railroads can't carry a tenth of what they do today, and even at that the rails deform so quickly that they have to be replaced in just a few months in high traffic areas.
See what reading books gets you? You won't learn stuff like that watching videos on Utoob.