Actually you should perhaps read your own source. To the extent the Forty-Eighters are even mentioned at all, the author notes in his intro:
Though they failed to break the power of the aristocracy in Germany in the 1840s, they contributed enormously to Lincoln's counterrevolution in the 1860s to break the chains of the Constitution and establish a powerful and dominant federal government.
We have a big problem there, and not just the author's reference to "Germany", a country that did not yet exist. He's got these people first resisting the chains of aristocracy (which is essential Liberalism) and then turning around and working to establish the chains of a powerful State (which is the opposite). He doesn't go into detail about how they were supposed to have effected this sudden about-face, which at that point was probably his best course considering he had just painted himself into a rhetorical corner.
But "National Socialists" as a proper noun --- which IS what you typed --- means Nazi, which is short for
Nationalsozialistische Deutsche Arbeiterpartei, the official name of the Nazi party in German, "nati" being pronounced "not-see" in that language. So yes you did.
If you had meant socialists who were nationalists and not affiliated with a party that did not yet exist, then you would have typed it in lower case. But that's not what you did -- you used the proper noun. Twice.
The Forty-Eighters were nationalists (small N) in that they wanted to coalesce the variously confederated states into a unified Germany (which would happen later) -- and they also may have been socialists, which was a new and trendy idea at the time. But they were not "National Socialists" (capital N) because that means Nazi, and that party, like the country of Germany,
did not yet exist.
Even the author of that book cannot be stupid enough to suggest Nazis visited the Americas a lifetime before they existed. HIs title is using a metaphor. It's not intended to be taken literally.