This is a very broad topic, but in a nutshell, Mahan believed international relations were decided by a command of the sea, he illustrated this often by the example of the growth and development of...
His writings influenced leaders of nations.
He was simply a USN staff officer.
Alfred Thayer Mahan was not only a naval officer but also a historian. He believed that the key to a great nation rested on a powerful navy.
Trading between countries.