Ukraine's shock invasion of Kursk takes away one of Russia's biggest advantages and may force it to rethink how this war is fought

• Ukraine is assaulting Russia's Kursk region, altering a war that had really only been fought in one country.
• Russia had advantages, allowing it to focus on Ukraine instead of giving its border heavy resources.
• The shift could make Russia reevaluate, stretching its resources and somewhat leveling the playing field.

Ukraine's unprecedented assault into Russia threatens the sanctuary Moscow has enjoyed throughout much of the war, potentially forcing the Kremlin to rethink how this conflict is being fought.

George Barros, a Russian military expert at the US-based Institute for the Study of War, which has closely monitored the war, said that Ukraine's advance into Russia's Kursk region will push Russian military leaders to take certain things under consideration that they have not had to since the launch of the full-scale invasion in February 2022.

Russia and its president, Vladimir Putin, have not invested significant resources into protecting the country's border, instead focusing on putting troops into Ukraine.

Ukraine is far smaller than Russia, and until it recently proved otherwise, it seemed to lack the capacity for any notable offensive into Russian territory. Additionally, its Western allies have put restrictions on how Ukraine can use the weaponry they provide. Russia has thus had a kind of sanctuary at home, making it seemingly unnecessary to send troops and weapons to defend its long borders.

But the invasion of the Kursk region is now "challenging and invalidating some of Putin's planning assumptions for what it takes to fight this war," Barros said.

He said that over the last two years, the Russian military had decided "to not protect the border region in northeastern Ukraine."

Barros said there were around 620 miles worth of border "that the Russians have not adequately manned, not defended in depth, and so on and so forth."

He explained that "the Russians really have had the luxury of not having to defend that border, and they've been able to use the men that otherwise would be protecting that border in operations elsewhere in Ukraine."

That appears to be changing and could, as a result, change the nature of this war, he said.

Ukraine advanced into Russia

Ukraine launched a surprise incursion into Kursk on August 6 and by Monday, had control of more than 480 square miles of Russian territory, according to President Volodymyr Zelenskyy.

The development is hugely embarrassing for Russia. The amount of territory that Ukraine's commander-in-chief said the country had captured within the first week was almost as much territory as Russia had captured in Ukraine in the whole of 2024 so far. Ukraine surpassed that figure on Tuesday.

The shock move massively contrasted with Ukraine's typical way of fighting Russia.

Ukraine's previous attacks on Russia typically only targeted specific military assets and didn't involve any troops actually crossing into Russia. Instead, drones and long-range weaponry hit military bases and stores, aircraft , and oil refineries .

Ukrainian soldiers described an easy crossing into the country, a sign Russia was not adequately protecting its borders.

One Ukrainian deputy commander involved in the invasion said that the soldiers guarding the Russian borders "were mainly kids doing their mandatory service," and other Ukrainian service members told the BBC that they were able to enter easily.

Russian troops are starting to be stretched

Barros said that Russia's need to rethink how it protects its borders is a long-term consideration, partly because doing it at scale will take time and partly because the amount of effort Russia needs to put in will depend on how much territory Ukraine keeps and holds.

But Ukraine is already finding success at stretching Russia's troops, he said.

He said that Russia needs to carefully consider "which units from along the front line in Ukraine are going to be redeployed to go to Kursk."

Those decisions are still in the early stages, he said, but reports and open-source information indicate that Russia has pulled some troops from some of its lower-priority fighting areas in Ukraine.

This includes units being pulled from Kharkiv in northern Ukraine and some other areas, like Kherson, Zaphorizia, and Luhansk.

US officials told CNN last week that Russia appears to be diverting thousands of its troops from Ukraine into Kursk. And a NATO country said that Russia moved troops from its enclave of Kaliningrad to Kursk.

Barros said Russia has not been observed taking forces from its priority areas in Ukraine's east, in Donetsk, where Russia is gaining ground. He said he doesn't "expect the tempo of operations there to decrease" anytime soon.

Warfare experts have told Business Insider that stretching and straining Russia's forces is likely a motivation for Ukraine's invasion of Kursk.

Barros said that "if the Russians do indeed decide they have to redeploy a lot of forces and properly defend an additional thousand kilometers worth of border, that's a substantial change because that is not a trivial amount of manpower and resources that now have to get bogged down for a larger undertaking."

"It will reduce the Russian command's flexibility for planning operations within Ukraine," he said, "and ideally, in the long run, it will drastically increase the cost of protracting and extending this war."

Russia has had huge advantages

Barros said that the time Russia spent not protecting its borders demonstrates how much of an advantage it had for so long.

He described Moscow as being "the beneficiary of a laundry list of luxuries" that allow the Russian military to focus its resources on Ukraine." These luxuries include how Ukraine is not allowed to use some Western weapons on Russian territory, he said.

Additionally, for Russia, he said, "there's a minimal requirement to protect the home front, minimal requirement to conceal any of the activity that it does. There's very few costs for sustaining and protecting, and that's kind of the sick irony of it, right?"

He said that Ukraine, on the other hand, has to invest heavy resources into protecting its power stations, rail lines, airspace, and aid arriving from the West.

"The Russians categorically don't have to really deal with any of that," Barros said, the only real exception being Ukraine's drone attacks that pale in comparison to the strength of the weaponry Russia uses against Ukraine.

He said the West should remove the weaponry restrictions it puts on Ukraine. "If we were to remove all of those advantages, then it forces the Russians to have to spread the resources," Barros said, noting just how unfair of a fight this war has been.

"Russia is a belligerent and a combatant in the war under the norms and laws of armed conflict," he explained, adding that the "Ukrainians are fully within their rights to take the war to Russian soil to engage in legitimate military actions on Russian soil. So far, for the most part, Russia has enjoyed a relatively cost-free waging of this war for two and a half years."

But the situation now is a rapidly changing one, and how it will end is unclear.

Rajan Menon, a senior research scholar at Columbia University's Saltzman Institute of War and Peace Studies, told BI Ukraine's actions may flip how the war is fought.

He said that Russia, with its much larger force, so far has been able to stretch Ukrainian forces along the front lines and put them under great pressure. Now, "in some sense, the Ukrainians have turned the tables," Menon said.

He said it's not clear what will happen in such a fast-paced operation and how it will play out.

But so far, he said, for Russia, "it is a moment of embarrassment because it shows the Russian response to this — whether in terms of evacuating people or dealing with this Ukrainian incursion on multiple fronts — has been disastrous. There's just no other way of putting it."

Barros said that so far, the invasion of Russia has been a win for Ukraine after it spent months on defense, holding against Russian attacks with little territory changing hands.

Ukrainians, he said, "are no longer stuck in the rut where they no longer have the initiative."

"It is now no longer the Ukrainians lying on their back for nine plus months at a time simply trying their best to triage," he said, and "deal with a buffet of bad decisions and dilemmas that the Russian command was serving up for them."