In the midst of this weekend's mayhem in Ukraine, one outcome will become inevitable given Russia's decision to intervene.

When the confrontation ends and life returns to normal, there will be a new western frontier along the River Dnieper and Russia will have imposed its suzerainty in the Crimea, thereby safeguarding its crucial naval assets in Sevastopol. This has little to do with the defiance shown by the pro-Russian president Viktor Yanukovich and even less to do with the presence of Russian-speaking gunmen at key points in Ukraine, including the airports at Sevastopol and Simferopol.

Far from being a mindless land-grab by the Kremlin, the protection of Russian interests in Ukraine is a matter of serious realpolitik for president Vladimir Putin. Ever since the end of the Cold War and the break-up of the Soviet empire, Ukraine has been a weak link in Russia's western defences and a potential ally of the West through its historic links with Poland and the old Austro-Hungarian Empire.

That helps to explain Putin's response to the current crisis - the scrambling of warplanes; the granting of asylum to Yanukovich; the menacing and the threats aimed at Kiev and the backing of local Russians in the Crimea, all classic intimidation tactics from the Soviet era.

Yesterday a Kremlin spokesman upped the pressure when he stated that a plea for help from the pro-Russian Crimean leader Sergiy Aksyonov would "not go unnoticed". Putin seems to be saying that he has the power and the capacity to make life difficult for the interim administration in Kiev, which he has castigated as a bunch of criminals or terrorists intent only on breaking up the country's autonomy.

The Russian tactics can be compared to what happened in 2008 prior to the invasion of Georgia and that has led to calls from Ukrainians for western intervention. But this time around there are differences. Not only was Georgia ten times smaller, but the Russian intervention did not risk a civil war as would undoubtedly break out in Ukraine. Then there is the position of Crimea, the predominantly Russian peninsula on the Black Sea which has been an autonomous republic within Ukraine since the end of the Cold War.

This is the real prize and one which Putin will not give up lightly. For a start, the port of Sevastopol is home to Russia's Black Sea fleet which leases the facilities - renewal of the lease is planned to take place in 2017. The warships are a powerful strategic asset giving Russia the capability to project its naval power into the Mediterranean. Before being ousted, Yanukovich agreed that the lease should be extended for a further 25 years but this proved to be unpopular with many Ukrainians who resent the Russian presence.

Nevertheless, despite the uncertainty Sevastopol is very much a Russian naval port and treated as such by the 15,000 resident Russian sailors. There is also a substantial local population of retired naval officers, attracted by the benign summer climate, who have bought homes in the area and add to the local economy. Add this to the local Russian population, which is the majority ethnic group in the Crimea, and it is not difficult to see why Putin is taking an interest in what is happening in Ukraine and wants to protect Russian interests. To do otherwise would be to ignore the risk to Moscow's global standing by showing that Russia was powerless in the face of a descent into anarchy in a neighbouring state which also happens to house a powerful naval asset.

So, to a certain extent, Putin has to be seen to be doing something if he is to retain his standing. On one level, it makes sense to make that move in the ultra-Russian environment of the Crimea where he can portray himself as the protector of their interests. His longer-term policy probably envisages the transformation of the autonomous republic of the Crimea into an independent or quasi-independent state which relied on Moscow's patronage. Not only would that safeguard Moscow's naval strategy but it would also send a message to the rest of Ukraine that their best interests might not lie in looking westwards towards the rest of Europe, but in throwing in their lot with Russia.

Either way it is a high-risk strategy. Russia's intervention in Georgia was tolerated because in an age of terrorism the situation in the country was deemed to be a security risk. No such problem exists in Ukraine, which is still viewed by many Russians as a friendly neighbour bound by strong historical and cultural ties.

By the nature of any military intervention there is always the danger of escalation and the last thing Putin needs is the outbreak of a civil war on his country's doorstep. That is the only thing that will keep him in check.