This is not an American flagged ship.
By treaty, which both the U.S. and the Marshall Islands agreed to (and enacted into law), the U.S. has to protect all Marshall Island flagged ships just as the do American flagged ships.
No it doesn't. It means we would protect them if invaded. Iran seizing a ship that has no connection to the Marshall Islands whatsoever except on paper in not an invasion. And I certainly don't understand this desire to go to war over the Maersk Freakin' Tigris.
No it doesn't.
The Government of the United States has full authority and responsibility for the security and defense matters in or relating to the Republic of the Marshall Islands.
I hate to be dense, but I'm having trouble understading you. Which parts of the law are you having trouble with? "full authority and responsibility?" "security and defense matters?" "in or relating to?"