Garry Kasparov is not a man you want to face in a battle of wits. In 1985, aged 22, he became the youngest ever World Chess Champion. Over the next 20 years, he would be the world's number one chess player for a record 255 months. A game he won in 1999, now known as Kasparov's Immortal, is considered the best chess game ever played.

Since retiring in 2005, he has devoted himself to politics. He formed his own political movement, the United Civil FrontA social movement that formed part of The Other Russia, an opposition coalition in Moscow. It advocated democratic elections, federalism and limits on presidential power., and helped organise the opposition to Vladimir Putin.

In 2013, he was forced to flee his country for fear of persecution.

A year later, when Russia invaded Ukraine and annexed CrimeaA peninsula in southern Ukraine that was seized by Russian forces in 2014 and annexed to the larger country., Kasparov was a lone voice calling for firmer action against the Kremlin. He warned that if Putin were allowed to get away with violating Ukrainian sovereignty, sooner or later he would come back for more.

Now it seems Kasparov has been proved right. And many are paying closer attention to what he is saying about Russia.

His message is stark. If the West does not stop Putin in his tracks, the risk of conflict - including nuclear conflict - will only increase. He warns that we must not allow ourselves to be paralysed by fear.

He claims the West has also violated Ukraine's sovereignty by preventing it from inviting allies to come and defend it. He thinks this indicates that NATO powers have effectively already declared Putin ruler of Ukraine.

But Ukraine is fighting back. It refuses to be handed over to the Russians. And in doing so, it has exposed the fear and inertia of the Western powers.

Now, Kasparov thinks the West must respond by reasserting Ukrainian independence. It should respond to Ukraine's calls for aid, set up humanitarian corridorsA temporary demilitarised zone intended to aid the transit of humanitarian aid into, or refugees from, a crisis region. and give Ukraine the weapons it needs to fight off the invaders and protect its people.

Others agree that if Putin is allowed to get away with his invasion, it could reshape the world order. They fear other countries might assume they can brutalise their neighbours without punishment.

Now, it seems, we are returning to a time where sovereignty can be dissolved at the point of a rifle.

But others think this is naive. They argue the world never really changed. After all, in 2003, the USA itself violated the sovereignty of IraqA country in the Middle East with a population of 43.5m. . It has tried to force regime change in countries like VenezuelaAn oil-producing country in South America. . The only difference now is that other countries are no longer respecting the rules.

They argue we have to respect the demands of realpolitikA German term that means literally "realistic" or "actual" politics. This is a system of politics based on what is practical and possible, rather than what is ethical or morally right.. Russia is a nuclear-armed state. Going to war would be a catastrophe. It simply cannot be constrained by the rules that we impose on less powerful countries.

Yes: Kasparov warned us in 2014 that Russia would be back for more. If Putin gets away with it again, there will be more provocations in future, ultimately leading to the war we all want to avoid.

No: We no longer live in a world with only one superpower. We have to face the reality: Russia is too powerful to be constrained militarily by the West. 

Or... Ukraine is already giving Putin a bloody nose, partly thanks to Western aid. We should have more faith in our sanctions and condemnations: the current strategy against Russia is working.

United Civil Front - A social movement that formed part of The Other Russia, an opposition coalition in Moscow. It advocated democratic elections, federalism and limits on presidential power.

Crimea - A peninsula in southern Ukraine that was seized by Russian forces in 2014 and annexed to the larger country.

Humanitarian corridors - A temporary demilitarised zone intended to aid the transit of humanitarian aid into, or refugees from, a crisis region.

Iraq - A country in the Middle East with a population of 43.5m.

Venezuela - An oil-producing country in South America.

Realpolitik - A German term that means literally "realistic" or "actual" politics. This is a system of politics based on what is practical and possible, rather than what is ethical or morally right.