By Aaron Kliegman Hitler may have been insane (at least strategically), but even he could be deterred. And indeed, he was, for a brief, instructive moment. The year was 1934. Hitler had been chancellor of Germany for 18 months and coveted Austria, his birthplace. So, the Nazi Party instigated a putsch to annex the land. Nazis assassinated the Austrian chancellor, Engelbert Dollfuss, attempting to seize power. In total, they killed more than 100 people and injured several hundred others. News of the putsch enraged Benito Mussolini, who was close to Dollfuss and not yet allied with Hitler. In fact, the Italian leader was hosting Dollfuss’s family at the time of the assassination. Mussolini had also declared strong support for Austria’s sovereignty. So, Mussolini moved the Italian army to the border between Italy and Austria, threatening Hitler with war unless the Nazis stopped their plot. And guess what happened next: Hitler backed down. The putsch failed. Mussolini of all people was the only one ever to deter Hitler. If only other European leaders had showed resolve to stop Nazi Germany before World War II broke out in full. There were certainly several opportunities to do so. In 1936, for example, Hitler ordered German troops to enter and remilitarize the Rhineland. (The order violated the Treaty of Versailles, which had ended World War I.) But Hitler also told his generals that, if France showed any signs of taking a military stand against the move, Germany should retreat. The French did nothing, afraid to risk going to war. All France had to do was demonstrate the smallest bit of strength to deter Hitler, who later admitted as much. “A retreat on our part would have spelled collapse,” he said. “The 48 hours after the march into the Rhineland were the most nerve-racking in my life. If the French had then marched into the Rhineland, we would have had to withdraw with our tails between our legs.” Hitler went on to explain that Germany’s military was weak and would have crumbled in the face of even “moderate resistance.” The same was true of the German military in 1938, when the Nazis finished what they started four years earlier and annexed Austria. In 1940, after war erupted, Hitler could have been deterred from invading France. Even then, Britain, France, and the US had far more military assets than most people appreciate today. They needed to rearm a little earlier and show a willingness to stop German aggression. Perhaps most striking, Hitler suggested during the war that he might never have invaded the Soviet Union in 1941 had he known about the Soviet Red Army’s T-34 battle tanks. In short, World War II possibly could have been avoided — either through deterrence or, more likely and preferably, by destroying Nazi Germany when it was weak. No, the world wouldn’t have been a utopia, but maybe it could have been spared a global cataclysm. Why does this history matter today? First, it proves that even the most crazy, irrational, and ideological tyrants can be deterred — that is, if the other side signals its capabilities and a willingness to use them. Second, it shows the tragedies that are possible if democratic countries don’t invest the necessary money in their militaries and are unwilling to exert their power early against expansionist dictators. Stated differently, history demonstrates the folly of appeasement. Consider Iran, whose leaders are deeply ideological and, like Hitler, despise Jews and seek the Anglosphere’s demise. While Barack Obama was president, the Iranian regime never feared for a moment that the US would attack Iran. The Obama administration established no deterrence. Indeed, the administration made clear that it sought to create cordial relations with Tehran by making concessions, believing that, through more intimate ties with the West, Iran’s leaders would moderate over time. That’s how Iranian negotiators secured such an advantageous nuclear deal for the regime, one that paves a path for Iran to obtain nuclear weapons. At the end of negotiations, for example, Tehran demanded an end to the embargo on shipments of conventional weapons to and from Iran. The US rolled over and conceded, desperate for a deal. If the regime believed the US was willing to use military force, it never would have been arrogant enough to seek such a concession. If Joe Biden is elected president, he will continue the Obama administration’s posture toward Iran. He and his top advisers have said a Biden administration would seek to re-enter the nuclear deal, with the vision of creating a more peaceful relationship between Iran and its neighbors — and between Iran and America. Biden would be wise to consider the words of Wang Xiyue, a US citizen and PhD candidate at Princeton who was imprisoned in Iran from August 2016 to December 2019. Wang explains in a new essay that, before his imprisonment, he thought Obama should visit Iran and move the bilateral relationship forward. But after witnessing the regime’s “actual workings from the inside” for 40 months, his view changed. “Rapprochement is a fantasy,” he writes. “The Islamic Republic thrives on tension with the United States.” Indeed, he adds, the regime’s “survival and its elite’s prosperity require maintaining hostility” with the US. That means concessions will only invite more aggression and establishing cordial relations is impossible (at least with the current regime). Establishing deterrence, however, can contain Iran’s belligerence. And Iran can certainly be deterred. What’s required is, above all, a continued robust investment in military power and a demonstrated willingness to use it. The situation in the Middle East is far more complex, of course, but this is the broad foundation on which all else should rest. Such a posture doesn’t reject diplomacy but strengthens it. For negotiations to be genuinely fruitful, Iran must know the US is willing to impose costs, with American power casting a shadow over the proceedings. And no threat casts a larger shadow than that of military force. The main problem with Biden, at least regarding Iran, is a lack of credible deterrence to undergird the rest of his policy. When the nuclear deal was finalized in 2015, critics compared Obama to Neville Chamberlain, invoking Britain’s appeasement of Hitler. Chamberlain, the British prime minister, agreed to give Hitler part of Czechoslovakia in 1938, hoping that would satiate Nazi Germany’s appetite for war and prevent escalation. It didn’t. But Chamberlain saw his choices as either appeasement or war with Germany. If Britain had rearmed by then and demonstrated a willingness to use its military, however, then the West would have had more and better options. As the events of 1934 make clear, the historical analogy goes well beyond the Munich Agreement. Hitler showed not only the futility of appeasement with a committed enemy but also the efficacy of deterrence with one. Today, America has no more committed an enemy than Iran. We should draw lessons from the past and apply them to the present. Those who don’t will repeat previous mistakes. Joe Biden seems poised, if elected, to go down a familiar, disastrous road.