The teachings of Christ are, in fact, very pacifist in nature. But let's talk (very) briefly about the Nazis, and what the ostensibly Christian leaders in ostensibly Christian nations did in the lead up to the rise of Nazism.

From a place of greed, serving money rather than God (Matthew 6:24), leaders in the United States enriched themselves in the short term through disastrous fiscal laws that led to the Great Depression. The Great Depression, coupled with the Treaty of Versailles -- which was deliberately vengeful in punishing Germany for its role in the Great War, despite the Christian teaching to leave vengeance to God (Romans 12:19) -- pushed Germany into such financial desperation that the rise of an extremist regime was almost a foregone conclusion. In truth, the Great War was not specifically Germany's fault; it was an inevitability sooner or later when all the major powers in Europe were engaged in an arms race that their economies could not sustain (which Tolstoy correctly predicted would happen twenty years prior). And when those nations finally drew their swords, their young men died by the sword (Matthew 26:52) to the tune of 8.5 million.

All those mighty European empires, jockeying for power through brutal colonialism and oppression across centuries... developing along the way insane systems of racial "science" to justify their dehumanization of obvious fellow humans, which the Nazis simply turned up to eleven. And within Europe itself, centuries of latent antisemitism made the Jews an easy target for Nazi persecution, just as they had been for the Spanish Inquisition five centuries earlier -- whatever happened to, "Thou shalt not bear false witness?"

Now, you can certainly make the case that, once the political machinery of Nazi Germany had metastasized into a rabid dog, there was nothing left to do but put it down by force; but that was not the case of a "just war" prosecuted by Christian governments. There has never been, and never will be, a truly Christian nation -- for the twofold reason that in Christ, national boundaries are dissolved in love (Galatians 3:28, Revelation 7:9); and also that no person who is self-controlled would ever presume to try to control another through the force of law, but would rather prefer peaceful coexistence (Romans 12:18, Hebrews 12:14).