This is the first of a series of concise 'articles' trying to the find the answers to questions we couldn't find answered quickly to when we searched the web/watched the news.
Given fact: The United Nations has been prevented from agreeing any kind of military intervention in what could be a civil war (the fact it is a civil war is disputed) in Syria because of Russia blocking any motion. June 2012
Background:
Russia and Syria have a military alliance: The Syrian port of Tartus hosts the Kremlin's only naval base outside of the old Soviet Union [wikipedia]. Russia also sells arms to Syria, as widely reported in the Western press. Syria's geographical location is clearly militarily significant; it borders Turkey, Iraq, Jordan - Google Earth below.

Possible current political reason: President Vladimir Putin feels that the West duped him into a de facto sanctioning of the Libya invasion (Russia abstained form the United Nations vote). [source]
Western journalists are prevented from legally entering Syria so it is impossible to know exactly what is going on in the country.
One journalist, a Russian national, Anhar Kochneva, reports the following:
"I’ve been living permanently in Syria for the last seven months, and I saw only three ‘so-called demonstrations’. So-called, because there were very few people and they were clearly staged as a performance for journalists." Anhar Kochneva [source]
"There are a lot of soldiers of fortune among the bandits. They are Chechens, Romanians, French, Libyans, and Afghans.
Moreover, there was a very funny accident with Afghan soldiers. A few Afghans were caught and asked, ‘What are you doing here?’
They replied, ‘We were told that we came to Israel, and at night we are shooting at Israeli buses. We are
fighting with the enemy to liberate Palestine.’ It might be funny, but it is true. The guys were really surprised, ‘Are we in Syria? We thought we were in Israel!’" Anhar Kochneva [source]