Final answer:
Alfred Thayer Mahan was the U.S. naval leader who advocated for building a strong American naval power in his 1890 work, which resulted in the expansion and modernization of the U.S. Navy, making it the third strongest in the world.
Step-by-step explanation:
The U.S. naval leader who first urged government officials to build up American naval power was Alfred Thayer Mahan. Mahan, a naval theorist and historian, emphasized the importance of naval power in his seminal work, The Influence of Seapower upon History, published in 1890. Recognizing the lamentable condition of the U.S. Navy, Mahan advocated for a robust naval force, establishing a network of naval bases, and constructing a canal across Central America.
His influential ideas prompted the passing of the Naval Act of 1890, which led to a significant expansion and modernization of the U.S. Navy, propelling the nation to thethird-strongestt naval power at the time. This strategic military development was a key element in advancing the United States' ability to project power globally and secure its emerging empire.