A Daily Beast article by Jamie Dettmer asks if what's happening in Syria could lead to World War III? It makes a good argument for the possibility of drawing Europe, Russia, Iran, the U.S., Israel, etc. into a larger war, maybe regional, maybe larger.
Many Americans would argue that this war started in 2001 on 9/11. Or perhaps the Long War began at least as long ago as the 1983 truck bombing of the U.S. Marine barracks in Beirut. Others would mark the beginning in 1979 in Afghanistan, against the Soviets.
Yet others would say the Long War began in 1948 with the establishment of Israel on land considered by Arabs as "theirs," and the attacks on Israel by neighboring Arab nations and by independence movements (e.g., Hezbollah, PLO, Hamas) off and on ever since.
My point is that the anti-Crusader Islamic militant movement has been underway for over half a century. The Long War didn't begin with the aircraft attacks on the World Trade Center and the Pentagon on September 11, 2001. Although that does mark when most Americans were forced to take it seriously.