Based on the provided information about Alfred Thayer Mahan, the statement that best describes him is:
"He was an American leader who was eager to expand U.S. influence especially by way of a strong U.S. navy. Mahan was a naval strategist and historian."
This statement accurately reflects Mahan's focus on the importance of naval power in asserting national influence and security, as well as his role as a significant figure in naval strategy and history. His theories on sea power greatly influenced naval policy and military strategy in the United States and around the world during the late 19th and early 20th centuries.