One Irish man, who is going to fight in Ukraine, says the battle goes beyond this conflict.
Ivan Farina, who is a veteran, will leave Ireland on Saturday and arrive in Ukraine on Sunday.
He told The Pat Kenny Show a defeat against Putin would have global consequences.
"I shall be leaving tomorrow and I shall be in Ukraine by Sunday.
"And the reason is to help put a stop to this madness, to finally - I suppose - rid us of the tyranny's that have sprung up, or have been allowed to spring up in the last 30 years.
"Ukraine has to survive, but it's not only about Ukraine - it really isn't.
"Those 40 million Ukrainians deserve the freedoms they have, and they're the same freedoms we have.
"They are making a good go of it and sharing, and that's what makes them a threat to someone like Vladimir Putin.
"But if Putin loses this one he will fall; and if he falls, the dictators around him they will fall.
"So this has potentially global consequences - not just for Ukraine, but for the whole world - so it's an important moment to step up."
'Such global unity'
Ivan says he has never seen the world as united as it is right now.
"I think the response globally has been absolutely tremendous - it has been just incredible.
"This is epochal, in all of human history there's never been such global unity.
"And I think every dictator and every tyrant around the world is now realising they can't stop their own people from hearing this, they can't stop their own people from believing that actually they have as much rights as anybody else.
"So there's a big point to prove by winning this war, and I think everybody knows that".
Mr Farina is no stranger to conflict, having fought in Bosnia with the Croatian Armed Forces in 1992 to 1995 where he lost an eye.
And he says a lot of people who have fought elsewhere are joining him in Ukraine.
"I'm not alone - as soon as I announced my intention to go, every messaging app I've got lit up with people I haven't heard from in years, saying that they're doing the same thing.
"These are guys that have a lot more experience than I do - they've been in Iraq, they've been in Kosovo, they've been in Afghanistan.
"Some of them have even been training resistance fighters in Myanmar, and they're all coming.
"I cannot emphasise how motivating this conflict is for people - if they have the skills, if they have the determination - they are determined to do something.
"I'm not a fool, I know what war is - only fools and thieves treat war as a game - and I know what we're facing, and it's not going to be good.
"There's nothing we will be experiencing or subjected to that women and children in Ukraine are not experiencing and being subjected to right now.
"And if they can do it, I think a thick-hyded old soldier like myself has a duty to take some of that onboard and save someone else the suffering".