KYIV, Ukraine (AP) — Ukrainian President Volodymyr Zelenskyy said no one knows how long the war in his country will last but that Ukrainian forces are defying expectations by preventing Russian troops from overrunning eastern Ukraine, where the fighting has been fiercest for weeks. In his nightly video address, Zelenskyy said he was proud of the Ukrainian defenders managing to hold back the Russian advance in the Donbas region, which borders Russia and where Moscow-backed separatists have controlled much of the territory for eight years. “Remember how in Russia, in the beginning of May, they hoped to seize all of the Donbas?” the president said late Saturday.