See the 75 million owner-occupied homes, the bountiful farmland, the 260 million vehicles, the hyper-productive factories, the great medical centers, the talent-filled universities, you name it--they all represent a net gain for Americans from the barren lands, primitive structures, and meager output of 1776.
For instance, on the day Trump issued the executive order temporarily banning even legal immigrants from certain countries from entering the United States, Buffett was at Columbia with his pal Bill Gates, telling students that immigrants should be welcomed.
In the same passage where he praises immigrants, he tells us that they, combined with our market system and the rule of law can "deliver abundance beyond any dreams of our forefathers." Why mention the rule of law?
So far, Trump's biggest executive order initiative, the ban on immigrants--especially non-Christian ones--from specific countries has been at least temporarily halted by the rule of law, as the order faced lawsuits from many directions, including the entire state of Washington, and judges around the country ordered immigration officials to stop barring legal entry while these suits are decided.
For example, in his letter, he refers to GEICO as "the company that set my heart afire 66 years ago (and for which the flame still burns)." If you take the long view, he argues, investments in a basket of solid companies with good financial underpinnings will almost certainly go well.