Thats interesting, I wonder if secessionist movements in the US would be viewed the same as a "group of people stealing his land".
I think what is or was unique about America, was its radical beginnings and subsequent radical ideas at least expressed through certain individuals. Thoreau's ideas, for example, was integral toward independence movements in the 20th century, the Anti-Federalists during the colonial period, and of course other american individualists responsible for general anti-statism.
Spain was in fact, a Kingdom. Kind of still is. Franco's party was never purged, and that civil war was actual won by the fascists. So talking to someone who considers themselves "small government" and "freedom loving" who believes a secession movement is "treason", just seems to be the Spanish version of a right-wing Republican in America that uses the liberty terminology. Most of them consider The South "traitors" to America.