What’s their agenda? Is it to protect Saudi Arabia or to thwart terrorism?
To ensure Iran's takeover of Iraq.
The mission will be somewhat defensive
First you musts learn and believe that Iraq is no more. There are three separate countries. That territory that was Iraq and Syria and now ISIL, the Kurdish lands, and the remaining lands around and south of Baghdad are the three.
The boundaries and especially the border cities have not been firmed up. The mission of the Marines is to beef up the Kurdish forces to solidify the boundaries and insure the desired border towns/cities are firmly under Kurdish control. Especially in fact mandatory, are Mosul and Kirkuk.
It may be that the mission is the same but the control is around Baghdad. I think the mission is Kurdish related.
No one dare mention this actual fact, but it is true. The talk about eliminating ISIL is very limited, to resolving the borders..... nothing more
There is no Saudi Involvement but there can be fair degree of certainty there is no Saudi opposition. The action is in essential correcting a mistake made in 1917 when the Brits and the Frogs carved up the Ottoman Empire