Russian soldiers patrol a village in the Russian-Ukrainian border area of Russia's Kursk region in a photo taken from video released by the Russian Defense Ministry.Russian Defense Ministry Press Service photo via APRussia has taken back some of the territory that Ukraine seized in Kursk.Warfare experts said it was territory that's easiest to take back and it will get harder for Russia.Ukraine can strategically pick where to defend but still has a big challenge ahead.Russia's retaking territory in Kursk, but efforts to drive the Ukrainian forces out of the country will likely only get more difficult.Ukrainian troops invaded the Kursk region in southwestern Russia in August, and at one point, they held roughly 500 square miles of Russian territory.