A Ukrainian soldier of the 33rd assault battalion hides behind a tree after hearing the sound of a drone in the town center on August 16, 2024 in Sudzha, Russia.aras Ibragimov/Suspilne Ukraine/JSC "UA:PBC"/Global Images Ukraine via Getty ImagesUkraine 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.