13 years of civil war
Russia expands its military presence in Syria with an additional airbase that can accommodate fixed-winged military aircraft. The U.S. Department of Defense also confirms that Russia added S-400 surface-to-air missiles to its Syrian stockpile and armed its military aircraft with air-to-air missiles. According to Military Times, "A Pentagon spokesman expressed concern" these moves indicate Russia's commitment to aiding the embattled Assad regime as opposed to combating ISIL. No Syrian opposition groups including ISIL have combat-ready aircraft that require air-to-air missiles.
Sources: Fox News Military Times