In 2006 the U.S. was at war in Iraq. Some of the enemy forces it very much struggled to fight against were coming in through Syria. The same year Israel lost a war against Hizbullah. Its armored forces were ambushed whenever they tried to push deeper into Lebanon while Hizbullah managed to continuously fire rockets against Israeli army position and cities. Hizbullah receives supply for its missile force from Syria and from Iran through Syria. Its long-term plans to attack Iran and to thereby keep supremacy in the Middle East depend on severing Hizbullah’s supply routes. The sectarian Sunni Gulf countries, mainly Saudi Arabia, saw their Sunni brethren defeat in Iraq and a Shia government, supported by Iran, taking over the country. All these countries had reason to fight Syria. There were also economic reasons to subvert an independent Syria. A gas pipeline from Qatar to Turkey was competing with one from Iran to Syria. Large finds of natural gas in the coastal waters of Israel and Lebanon make such finds in Syrian waters quite plausible.
http://www.moonofalabama.org/2013/09/a-short-history-of-the-war-on-syria-2006-2014.html
