If, today, it's "no surprise" that Americans "start fighting each other"  it's not because they've "run out of things to exploit", it's because they've ALWAYS been that way (as you suggest early in your comment.)  They have always fought each other...blacks against whites--and the reverse--whites against Indians (and the reverse), immigrants--such as the Irish--against governments, and even each other. And that's just up to 1900, long before they ran out of "things to exploit."

See my own comment.