We know this because Russian troops annexed Crimea and Russia continues to actively support insurrection in the east of the country.
Over recent decades, Russia has been happy to destabilise neighbouring countries which it considers to be in its sphere of influence.
In recent days, Mr Putin has upped the rhetoric by suggesting that the conflict there looks like genocide.
Russia has repeatedly claimed that Kiev is being provocative, warned against Nato expansion to include Ukraine and deployed Russian forces close to the Ukrainian border.
Over the weekend, Mr Putin bemoaned the consequences of the fall of the communist USSR saying: “After all, what is the collapse of the Soviet Union? This is the collapse of historical Russia under the name of the Soviet Union.” The former KGB officer decried the disintegration of the USSR saying it remains a “tragedy” for “most citizens”.
The international community is now warning Russia about the serious consequences if they invade Ukraine. US President Joe Biden, who has held a virtual summit with Mr Putin, said if Russia went ahead there would be "economic consequences like none he's ever seen”.
Meanwhile, the G7 countries said: “Russia should be in no doubt that further military aggression against Ukraine would have massive consequences and severe cost in response.” Russia was called on to “de-escalate, pursue diplomatic channels and abide by its international commitments on transparency of military activities”.
No-one wants a new cold war with Russia but invading its Ukrainian neighbour (again) cannot go unanswered.