Launched on August 6, Ukraine’s surprise cross-border offensive into the Kursk region of Russia has startled the world. Not only is the operation far and away the largest Ukrainian attack into Russian territory since Russia’s invasion of Ukraine in February 2022; it also has come at a time when Ukrainian forces were struggling to preserve their already stretched resources along the existing 3,300-mile front. Yet as of mid-August, Ukrainian forces had penetrated dozens of miles into Russia and gained control of 74 villages and towns in the Kursk region, according to Ukraine’s top military commander. Ukraine has also taken more than 100 Russian prisoners.

At this stage, it is too early to assess the success of the operation. So far Kyiv has said its primary aim is halting Russian artillery attacks from the Kursk region into Ukrainian territory. According to the Ukrainian government, more than 255 glide bombs and hundreds of missiles have been launched at Ukrainian towns from the region since the beginning of the summer. Kyiv also hopes to use the POWs in a prisoner exchange to release Ukrainian soldiers from Russian captivity. Even more important, the operation could force the Kremlin to redeploy some of its troops from southern and eastern Ukraine. Previously, it was Ukraine that had to draw from its existing deployments to counter Russian attacks.

Politically, the Kursk offensive serves another purpose. It allows Kyiv to address its partners from a position of strength and puts the growing debate about potential cease-fire negotiations in a different light. Few Western observers expected any significant Ukrainian offensive this summer, let alone one that could penetrate well into Russia. If nothing else, Kyiv has demonstrated that it is very much still in the fight, easing recent concerns about its staying power. Moreover, Ukrainian troops have shown that they are capable of planning and unleashing a surprise large-scale offensive in total secrecy despite the presence of drones and satellites on the battlefield that can see almost everything.

This is a striking contrast to the first six months of the year, when the frontlines remained largely static despite intense fighting. By early 2024, citing a sense of impasse, many Western analysts were pushing for some kind of settlement with Moscow. Although there was no official support for this from Kyiv, some experts had also begun proposing ceding Ukrainian territory to bring an end to the fighting. Yet as recent events have shown, the war is not exactly at a stalemate: both sides have launched major actions since the late spring, and thanks to the arrival of new weapons and new defenses, the balance of power has shifted. Although much has been made of polls showing mounting war fatigue among Ukrainians, few are prepared to give up significant parts of their country to reach a settlement. Ukrainians are also wary of any plan that would freeze the frontlines where they are now, which would leave Russian forces on their doorstep and poised to launch a new invasion at any time.

Amid these concerns, the Kursk operation has also shown just what is at stake for Kyiv and why it is continuing the fight. Whether in the daily grind of the eastern front or in bold new offensives, Ukrainian forces are seeking to keep Russia off balance and to make the war far more costly—and above all, to prevent Moscow from strengthening its own war machine further.

To understand what the Kursk incursion means for Ukrainians, it is crucial to follow recent events in and around Kharkiv, the country’s second largest city and a crucial bastion of its northeast region. On May 10, the Russian army began a long-anticipated assault on the city, which lies near the Russian border and is home to 1.3 million civilians. Since the fall of 2022, when the Ukrainian army liberated this area, it had remained relatively calm by comparison with the east and the south, and many Ukrainians displaced from the Donbas had sought refuge there. A Russian occupation of even part of Kharkiv would have been a dramatic setback for Ukraine.

Yet that didn’t happen. During the early days of the May offensive, Russian forces moved five miles into Ukrainian territory, with heavy fighting in the border area around Kharkiv. But Ukrainian forces succeeded in halting the advance, and by by the end of the month, it was clear that the city would not be taken. Today, Russian forces continue to press the fight near Kharkiv, but the stalling of the offensive marks something of a turning point in the war this year: barring a cataclysmic change in the balance of forces, it is now highly unlikely that Russia will be able to capture Kharkiv or any other large Ukrainian city.

This outcome was not foreseen by Western observers. When Russia’s spring assault began,........

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