Final answer:
Alfred T. Mahan argued that sea power was essential for national greatness and influenced the expansion of the U.S. Navy in the late 19th century.
Step-by-step explanation:
Alfred T. Mahan argued in his book The Influence of Sea Power Upon History that sea power was essential to national greatness.
He believed that powerful and prosperous nations throughout history achieved their status through naval power. Mahan recommended that the United States should build a modern fleet of big ships with big guns and acquire strategic military bases and colonies to establish a network of naval bases and fueling stations.
His ideas heavily influenced policy makers and contributed to the expansion of the U.S. Navy in the late 19th century.