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Wladimir Klitschko and Vitali Klitschko, former boxing champions, rose to stardom through fighting in the ring. Now, the brothers will fight for their country. Wladimir enlisted in the Ukrainian reserve army three weeks before Russia's invasion early Thursday, and Vitali – the mayor of Kyiv, Ukraine – said this week he'd also take up arms. 

In a video posted to Twitter on Thursday morning, Wladimir Klitschko appealed for help in what he thinks will be a "senseless war" with no winners or losers. 

"I'm calling to all international partners to observe this tragedy that is happening nowadays in Ukraine," Wladimir said. " … I just want to tell you we must stay united against this aggression, against Russian aggression. Don't let it continue happening in Ukraine. Don't let it happen in Europe and eventually the world. United we're strong. Support Ukraine."

Also Thursday, Vitali Klitschko told Good Morning Britain he was ready to fight in what's "already a bloody war." Klitschko said "I don't have another choice" but to take up arms against Russian invaders.  

Russia invaded Ukraine early Thursday in what president Vladimir Putin described as a "special military operation." In a speech that morning, Putin said he intended to "demilitarize" the country as opposed to occupying it. 

Two hours after Vitali Klitschko's announcement, his brother chimed in with a tweet explaining how dire the situation is for Ukraine and beyond. 

"The world is watching how reckless and deadly imperialism is, not just for #Ukraine but the whole world," Wladimir wrote. "Let history be a lesson to not be repeated." 

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