Good summary and I share your observations. I was rather disappointed, because I had liked some of Huntington's other work. But this seemed grossly a-historical, a bit hysterical and weirdly aimed at proving that the only "good" American is a white Protestant one. As someone who lives in the oldest town in the US, founded by the Spanish (gasp!) in 1565, I also thought that for a historian he had strange gaps in his history.
The oldest city in America is Mexico City - founded long before Columbus. Maybe you would like to move there?
Despite your user name it is you seem to take "a-historical" position. USA is a product of Protestant/British culture. If WASP core disappears USA will not last very long.
Same was with the Roman Republic - it decayed and dissolved when the ethnic Latins who created it lost their demographic strength and cultural identity.
Yeah, and he neglected to point out that if it wasn't for the Spanish, we'd never have gained out independence. However, because the Spanish were, uh, Catholic, that doesn't make it into our history books.