There is more cause for U.S. involvement then there has been for either of the last two Iraq wars, or Syria. If ISIS isn't stopped, then every NATO soldier who died following the 2003 invasion died in vain.
I hate to say it because we are 17 trillion in debt, but I think we should start a full-scale ground war against ISIS. They are organized more conventionally than your average guerilla terror fighters so they should be easier to stop. If we focus on taking out their forces the war may only last a few months. Plus, the U.S. looks very weak to the world right now, and a war could help our image and restore our influence in the Middle-East.
I respectfully disagree, for a number of reasons. Here's just a sample:
If we go to war with ISIS, we go to war with the Sunni, who are the overwhelming majority of the middle east, and are supported by our allies Turkey, Saudi Arabia, Qatar, etc. One of the reasons ISIS is so strong now, is that they have subsumed the support of secular Ba'athists and former Republican Guards. The reason these educated elites have resorted to ISIS is that they have been excluded by the Shiite al-Maliki from leadership positions in the Iraqi government and army. We could do much to defeat ISIS by giving these secularists more attractive opportunities in a unified Iraq.
If we go to war with the Sunni ISIS, we are in effect supporting the creation of an independent, militant Kurdistan. This will cause a whole new chain of problems for the region.
To effectively wage war against ISIS, we must have boots on the ground in Syria, not just Iraq.
The overall thrust of US policy since the early 90's has been to reduce stability and sow chaos. To further break up Iraq, Syria, and maybe even portions of Turkey and Armenia will only cause more instability and chaos.
A better plan to defeat ISIS might consist of shoring up support for Assad in Syria, deposing al-Maliki in Iraq, and clamping down on the funnel of money, weapons and men streaming in from Saudi Arabia, Qatar, Turkey and beyond.