Question: Why is Russia digging its heels in on Syria?

Russia is pursuing its own national interests in Syria and the most pressing of these is the fear that a rebel success could lead to further destabilisation of its own predominantly Muslim regions.

Pursuing national interests is the basis of what is known as the “realist” school of international relations, a school of opinion that has been around for a very long time.

In the 17th century, French chief minister Cardinal Richelieu intervened on the Protestant side in the Thirty Years War because the Holy Roman Emperor was getting too big for his boots. Richelieu may have been a cardinal but France came first.

In today's world Russia is not the only "realist". In the debate on Syria the United States has cited not only the horror of the use of chemical weapons but has declared that it could justify a military strike in pursuit of its national interests.

So what are Russia’s interests in Syria? There are, first of all, some important economic interests and there are geopolitical interests but the most emotive interest is the safeguarding of its own territory from infiltration by Middle Eastern extremists.

Economically the al-Assad government is one of Russia's best customers. Bashar al-Assad not only has ordered Russian armaments such as the S-300 missile system but in the past week he has started to pay for them.

This system will not work against an American cruise-missile strike because the Russians have held back on delivering key components. Russia is not supplying chemical weapons to Syria and a slip of the tongue by US defence secretary Chuck Hagel – which suggested they were – has aroused indignation in Moscow.

Politically Syria is Russia’s only ally in the oil-rich Middle East region that it sees as being dominated by the United States.There is a small Russian naval facility in the Syrian port of Tartus and there may be up to 30,00 Russian citizens in Syria.

Moscow is very wary of what might happen and who might take over if Bashar al-Assad is overthrown by rebel forces, some of whose elements are similar to, and supportive of, those carrying out an Islamist insurrection that is currently taking place on Russian soil.

Geographically Russia is much closer to Syria than many think. The very word Russia conjures pictures of the frozen wastes of Siberia, of Napoleon's and Hitler's armies wasted by a climate that the Russian and Soviet armies relished. But there is another Russia. This is the Russia of the Black and Caspian seas, of the Caucasus Mountain range and its predominantly Muslim population where an insurrection led by extreme Islamists in Dagestan has been in progress for a number of years. This Russia is almost in the Middle East and has seen in the past infiltration of its territory by Middle Eastern Jihadists such as Ibn Al Khattab from Saudi Arabia who became a rebel leader in the two Chechen wars. Russia looks at a possible rebel success in Syria as something that would encourage further instability in its own territory.