After Russian President Vladimir Putin claimed to have annexed large swathes of Ukraine on Friday, Ukrainian President Volodymyr Zelensky responded by saying his country had applied to join NATO. “We are taking our decisive step by signing Ukraine’s application for accelerated accession to NATO,” he wrote on his Telegram channel. Any application would require the unanimous support of the military alliance’s 30 member nations. Russia has previously threatened to retaliate against any countries that join NATO, accusing the alliance of waging a proxy war against Russia on behalf of the West. Some European countries had resisted joining in order to avoid ruffling Russia’s feathers but Russia’s unprovoked invasion prompted countries like Finland and Sweden to change their tune. On Friday, Zelensky said he was prepared to negotiate with Moscow—“but with a different Russian president.”