Do you know how or why a US soldier was killed "in action" for the first time since the official withdrawal of US troops in Iraq?

Most news agencies did not cover any particulars surrounding a soldier’s death nor the low-keyed operations taking place in Iraq. Iraq- the country where we (US) recently negotiated a treaty?
The Marine- from the branch of the military usually sent First into an area of instability, was working on a new type of facility for the battle against ISIS. The intel about this new type of facility was not due to be released to the public yet.
With the death of a highly trained Marine via a rocket blast on Saturday, the Pentagon was forced to agknowledge and reveal the information concerning the creation of the fire base in Iraq, where his death occurred.
No. Not- A Fire Base…..it’s A…fire base. ( only lower case! )

Have we just opened up a whole new level of troop involvement for the USA?
The information grudgingly released today by the Pentagon stated that it was to be turned over to those nationalist factions fighting ISIS. (sos about our “just establishing and then we leave” pattern.)
What in the world is this really about?
Did other nations participating in this Middle Eastern scourge know of these fire bases?
Was this done in conjunction with the cessation and withdrawal of Russian Air Force missions? .....A Next Phase, if you will, of anti-ISIS operations?
What gives?

see reference: U.S. sets up firebase in Northern Iraq http://www.cnn.com/2016/03/20/politics/us-firebase-iraq-isis/index.html