The supposed legal authority for American military interventions is a resolution by Congress authorizing the President to use military force to root out terrorists who attacked the United States on Sept. 11, 2001.
But after 14 years, radical terrorists such as Al Qaeda and its successors, including the so-called Islamic State (aka ISIS, ISIL and Da’esh), are stronger than ever. Why?
It is because the American military is invincible in destroying the governmental and economic structures of nations, but is incapable of establishing order.
This is partly by design. The so-called revolution in military thinking inaugurated under Secretary of Defense Donald Rumsfeld called for use of small, highly-mobile, highly-trained special forces with high firepower, instead of the mass armies of the World War Two area. Such forces are effective at killing people and breaking things but not at long-term occupations.
The other is that the U.S. government, being averse to committing sending large numbers of Americans into battle, supports extremist Islamic terrorists when they are fighting other designated enemies. This is what happened in Libya, and is the real reason for the Benghazi tragedy. It is what is going on in Syria now.
I think these linked articles provide good background.
ISIS is US: the Empire and the Evil Genie it released by Paul Street for Counterpunch.
Phyllis Bennis: ISIS Is Filling The Holes Left By The US War on Terror by Sean Nevins for MintNews.
Putting Out the Syrian Fire by Jo Comerford and Mattea Kramer for TomDispatch.
Hat tip for the links to my e-mail pen pal Bill Harvey.