In the days just before Turkey’s military incursion into Syria, for which the stated aim includes purging a Kurdish militia that has been allied with the United States in the fight against the Islamic State, President Trump made a comment on the history of the two conflicting sides. He defined Kurds as Turkey’s “natural enemy,” adding, “one historian said they’ve been fighting for hundreds of years.”

I am not sure who that historian was, but as someone who has studied this particular history, I can assure you that the tension between Turks and Kurds is not centuries old. It is actually about one century old, and it’s the result of a very modern force: nationalism.

The history does begin in the early 16th century, when the Ottoman Empire, founded in western Anatolia by Sunni Turks, began to expand eastward, only to conflict with the Shiite Safavid Empire in Persia. The Kurds, a tribal people, most of whom were Sunni Muslims, were caught in the middle; soon they willingly joined the Ottomans. Through the next four centuries, they lived under the same state with Turks, Arabs, Bosnians, Armenians, Greeks and Jews — because the Ottoman Empire, like the neighboring Hapsburg Empire, was a multiethnic and multireligious mosaic.

The Ottoman elite was mostly Turkish, but not Turkish nationalist. So Kurds never faced any denial of their identity. Their ancestral homeland was often called “Kurdistan,” which even briefly became the name of an administrative region in the 19th century. In the same era, there were a few revolts by Kurdish chieftains, but only as a reaction to the centralization of the state and the new taxes and obligations it entailed.

The watershed event was the proclamation of the Turkish republic in 1923 by Mustafa Kemal Ataturk. Unlike the multiethnic Ottoman Empire, Turkey became a nation-state that did not honor any identity other than Turkishness. Ataturk famously declared, “Happy is the one who says ‘I am a Turk’” — a motto still carved on public buildings and even mountaintops all across Turkey. But many Kurds didn’t feel happy with this dictate. One revolt followed another, only to be suppressed brutally.

The Turkish republic, in other words, is guilty of disrespecting its Kurdish citizens, banning their language — even outlawing their music — and crushing their political movements, for decades and decades. And with this mindless authoritarianism, it consolidated its worst fear: Kurdish nationalism.

The latter force exploded in 1984 with the rise of the Kurdistan Workers’ Party, known as the P.K.K. — a terrorist army that combined Kurdish nationalism with Marxist-Leninist ideology and Maoist guerrilla tactics. To some Kurds, this made them freedom fighters. But other Kurds, who opposed the organization, paid with their lives. As is typical with national liberation movements, the P.K.K. defined itself as the only vanguard for the people, showing no mercy to “traitors.” The brutal war between the P.K.K. and the Turkish republic has continued to this day, leaving behind more than 50,000 casualties.

Yet the Turkish republic corrected some of its mistakes. The senseless bans on the Kurdish language were lifted first in the early 1990s by the great liberator Turgut Ozal and then in the 2000s by Turkey’s current leader, President Recep Tayyip Erdogan. In 2009, Mr. Erdogan even initiated peace talks with the P.K.K. Yet during those negotiations it became clear that the P.K.K. wanted not just more rights for Kurds, but also a territory to rule — single-handedly and hierarchically, with its party commissars and “village communes.”

Sadly, peace talks collapsed in the summer of 2015. This is partly because Mr. Erdogan couldn’t gain much from them politically. But also the P.K.K. never said it would put down its arms and instead threatened to extend what it called its “revolution” in Syria into Turkey. Since then, with his new ultranationalist allies, Mr. Erdogan has reverted back to all the hawkishness of the “Old Turkey” that he used to oppose — including jailing or ousting elected Kurdish politicians.

At the same time, the United States had entered the scene by deciding that the best asset against the Islamic State in Syria would be the Kurdish People’s Protection Units, a militia of the Y.P.G., which, according to the C.I.A. World Factbook, is the Syrian wing of the P.K.K. Turkey strongly objected to this plan to “defeat terrorists with other terrorists,” but the Obama administration didn’t mind. Soon “the Kurds,” without any nuance, become heroes in the West. Americans looked at Kurdish female fighters, and saw them as brave emancipated women. Turks, by contrast, saw them as comrades of Seher Cagla Demir, the Kurdish female suicide bomber who killed 37 people in downtown Ankara, and whose posters were put up in Y.P.G.-controlled locations in Syria.

That is why anti-Americanism has skyrocketed in Turkey in the past four years. And President Vladimir Putin has used it cleverly to lure Turkey’s leaders to his side.

Now the Turkish army is marching into northern Syria, to create a “buffer zone” between Turkey and the Y.P.G. While Turkey is indeed right to be concerned by a “P.K.K.-istan” beyond its longest border, it is unclear what this operation may really achieve — other than stoking nationalist sentiment at home, which may help Mr. Erdogan’s declining popularity. The idea of relocating more than a million Syrian refugees to this barren buffer zone is simply frightening.

The United States should help, not by unilaterally siding with “the Kurds” against Turkey, which will only further infuriate the latter, but by doing what the Obama administration should have done four years ago: Understand Ankara’s concerns, mediate between the two sides and broker a peaceful deal, an option President Trump suggested Wednesday.

For the longer run, both Turks and Kurds should finally grasp the century-old lesson: There is no “military solution” to this problem. Kurdish nationalists will not be able to carve out a Kurdistan from Turkish territory, nor will Turkish nationalists be able to “wipe out all terrorists.”

The only solution is to liberalize Turkey, to make it more respectful to its Kurdish citizens — in fact, to all its citizens — while curbing the totalitarian ambitions of the P.K.K. And while this seems far away from the current reality, there are saner forces in Turkey that may turn the tide.

Mr. Erdogan himself once spearheaded this idea during the peace talks, with a beautiful slogan that then became popular: “Let the mothers not cry.” Yes, let the mothers not cry anymore — neither Turkish nor Kurdish ones, neither in Turkey nor in Syria.