I believe it's fair to say he refers to western civilization, founded basically on Judeo-Christian values, with most laws based on English common law. We became a country of western culture & a heritage of eastern Europeans. The indigenous tribes did not assimilate into the gene pool in any significant way in N. America (In C. Am. of course they did, since a mere 160,000 Spanish settlers eventually intermarried with about 8 million "indians"). In N. Am. they were, unfortunately, herded, isolated, moved, and systematically killed. They were considered savages - a culture which was viewed as primitive. A blot on our history to  be sure, but the gene pool became predominantly European.
It's neither unusual nor unreasonable for many to want to retain our identity, our culture, our norms, our laws, our values - which many believe are largely responsible for our success.  You may call them nationalists or even palio-conservatives.   You may not call them wrong, for that is opinion.