Putin has made it clear that Russia and the United States don't see eye to eye when it comes to Syria.
Russia and Syria are longtime allies. For one, just take a look at their weapons deals. Between 2007 and 2010, Russian firms selling weapons to Syria made almost $5 billion.
It would be costly for Russia to end that relationship, analyst Peter Fragiskatos told CNN earlier this year
"Russia's leadership still sees much to lose economically and strategically from cutting Syria loose," Fragiskatos wrote. "Russia sees Syria as another test case for the West's appetite for intervention, and views the danger of U.S. involvement as a direct threat to its own interests."
There are other reasons to suspect Russia will keep supporting Syria. Russia's only naval base in the Mediterranean is on the Syrian coast, and Putin is still upset about NATO's bombing in Libya two years ago that removed Russian ally Moammar Gadhafi from power.
8. What's religion got to do with it?
The al-Assad family is Alawite, a Shiite Muslim offshoot that's one of the minorities in a country that is nearly three-quarters Sunni.
Al-Assad has filled key positions in his government with extended family members, and many of his supporters are Alawites and other minorities who fear what might happen if the Sunnis were to gain power.
Because the Syrian regime is Alawite and the majority of the country is Sunni, there are concerns that Syria could spiral into even more violence.
9. What's the worst that could happen?
In a worst case scenario, experts say, the fighting could spill over and make trouble for Syria's neighbors -- threatening stability in a part of the world that's already known to be volatile.
Surrounding Syria are Lebanon, Iraq and Jordan, Israel and Turkey. The violence has been prompting war refugees to seek safety in some of these nations. In Turkey, there are ethnic tensions involving Kurds who live along its southern border with Syria.
All of these countries have a lot of religious, cultural and historical issues between them that add countless layers of complexity to the crisis. And when an entire region of the world loses stability, that worries the international community as a whole.