2016 Presidential Election ring a bell?
So you think Steve Bannnon is going to run for President?
Easy answers.
1) without the United States intervening on the global stage the horrors of the 20th century would have been significantly worse
I believe that is demonstrably wrong. In fact it is an exact consequence of our interfering with world affairs that caused most of the horrors of the 20th Century.
Woodrow Wilson getting us into World War II caused the Germans to lose the war. Had we stayed out of it, they would have won or tied. The British and the French would not have been able to force on them the devastating conditions that wrecked their economy and caused the rise of Hitler.
No Hitler, No World War II, No Holocaust, No Mao, No Khmer Rouge.
Americans staying out of World War I might have prevented Lenin's return to Russia, stopped the Holodomor, and all the suffering of the Russian people and the Eastern Block.
No Korean war, no Vietnam.
No Atomic bomb, no Nuclear proliferation.
Also no sexual revolution and no abortion.
Over 100 million dead would likely have been avoided.
You could not likely have achieved a worse loss of life in the 20th century than what we did experience, and all because we meddled in affairs that were none of our business.
2) tariff wars, inflation and the great depression
You think a "tariff war" caused the great depression? How about "easy credit", and the boom and bust conditions which are a normal part of traditional economic system?
You also leave out the fact that the Government meddling in the economy caused a momentary recession to prolong itself far longer than it would have had they used the same methodology as "Silent Cal" to deal with it.
3) Nationalism is exclusionary.
So are borders. In fact borders exist for the explicitly purpose of protecting those people within them as a "nation."
..it is the antithesis of Patriotism.
The word "Patriotism" is derived from the word "Pater", which is Latin for "Father." It literally means "love for the land of my father." It does not mean "Universal love for all lands."
nationalism gets you 1940's Germany and Italy.
Says who? You've been listening to too much left wing propaganda. Of course since it has been ubiquitous since Word War II, It's hardly your fault, but still you should not simply accept stuff the left says without a grain of salt.
The Communists seized upon the "nationalist" aspects of German and Italian Fascism as the cause of their fascism. No, the International Communists were just as Fascistic, but pointing out "Nationalism" gave them a means of distinguishing themselves from the obviously evil Nazis and Italian Fascists.
The Communists were in fact worse.
"Nationalism" was in fact the argument the North asserted to justify their effort to prevent independence of the South. Some would claim that in this case, "nationalism" was a good thing. Weren't you earlier defending the 13th, 14th, and 15th amendments? Seems like they wouldn't have happened without this "Nationalist" fervor which was began in the 1860s.
..and the Soviet Union of the Cold War. U.S> Patriotism defeated all of those.
Patriotism and Nationalism are the same side of the same coin.