Such a demand cannot be pursued in a limited war, nor without the willpower to impose the peace for an extended duration.
Andy notes the ridiculousness of Tucker Carlson’s claim that “unconditional surrender means foreign troops get to rape your wife and daughter.” Carlson’s claim makes more sense if you see history solely through the eyes of Nazi Germany. German women in 1945 did face a brutal campaign of mass rape when their country fought to the bitter end. Even then, however, that campaign was conducted by the Soviet Red Army — not by the armies of the Americans and other Western nations. Nor did we perpetrate mass rape in Japan, or in the South during Reconstruction, nor in any other American war. (Of course, rape, murder, robbery, and other abuses of civilians do happen in wars from even the best of armies, which is yet another reason not to send armies to war lightly. But there’s a huge difference between crimes that may or may not be punished by military superiors and an orgy of sexual abuse on a massive, state-sponsored scale.)
There are some broader myths about the concept of unconditional surrender. The phrase entered the common American lexicon as Ulysses S. Grant’s terms for the surrender of Fort Donelson in February 1862. It received much play in the Northern press at the time, due in part to the paucity of Union victories up to that time and in part because it fit neatly as a pun on Grant’s initials (which were themselves the product of a typographical error at West Point). Even then, Grant didn’t coin the term; it had been used by Andrew Foote, leading Grant’s gunboat support, at the preceding battle of Fort Henry, and the Fort Donelson ultimatum originated with Grant’s subordinate and old teacher, Charles Smith. It may also have reflected Grant’s particular and warranted contempt for Gideon Pillow, one of the Confederate commanders at Fort Donelson. In any event, demanding unconditional surrender of a fortification in a battle is rather a different matter than demanding it as the peace terms for an entire war.
Unconditional surrender became de facto the war policy of the Union, but one that Lincoln never openly embraced (to the contrary, he negotiated face to face with Confederate peace commissioners as late as February 1865). The Confederate government ended up dissolving and being captured one by one, rather than agreeing to any negotiated terms. Individual armies surrendered with only modest face-saving agreements such as parole of soldiers and retention of sidearms; when William T. Sherman agreed with Joseph Johnston’s army on terms binding postwar political conditions, they were repudiated by the government in Washington. The war was thus, in effect, prosecuted to a complete submission and the destruction of the Confederate regime. Of course, that also reflected the view of Lincoln and his party that the war was an internal rebellion, in which the Confederacy had no legitimate legal status — certainly, none that would survive the war. The war, and the peace, were successful in most of their aims: the Union was restored, slavery was abolished, neither secession nor organized rebellion has been seriously attempted again, and the South was, within a decade, fully reintegrated into our political institutions. That said, it took a decade-long occupation, and due in good part to the terrorist insurgency of the Klan, it took another century after Reconstruction to purge the South of systematic defiance of the constitutional guarantees of equal rights for black Americans.
Franklin D. Roosevelt revived unconditional surrender in remarks in 1943 that developed enough inertia to become American and Allied war policy regarding both Germany and Japan (Italy left the war well before that, also having destroyed Mussolini’s regime). A key impetus to translating FDR’s impulses into Allied policy was the shared sense that the cataclysm of the First World War had not been pursued to a sufficiently decisive end to deter its repetition. The policy was pursued to the end in both cases. Little more than a fig leaf was offered to the defeated powers. It is sometimes objected that the Japanese surrender was not entirely unconditional, as the emperor was retained. But the imperial prestige and influence that was built up between the 1860s and the war was entirely demolished, leaving the emperor once again (as he was from the 1190s to the 1860s) a purely symbolic figurehead, while the rest of the Japanese regime was replaced by a new constitutional democracy. Japan was prostrated, occupied, and — like Germany, and like the South — given no say or leverage in the terms upon which it would regain control over its own governance. Once again, a lengthy occupation was required (one that faced little or no violent resistance), and success in turning both countries into long-term allies rather than adversaries was total.
The advantage of unconditional surrender as a demand, in each case, was that it accorded with the American sense of war as a total pursuit of total victory, and delivered a genuinely lasting and stable peace. But the cost was high: such a demand cannot be pursued in a limited war, nor without the willpower to impose the peace for an extended duration. A war such as the current one with Iran may well be pursued to the point where no Iranian regime is left that could negotiate terms, but it will not result in a peace that looks like those of 1865 or 1945. Which is why it is silly for Donald Trump to be talking in those terms.