Final answer:
Alfred Mahan coined the phrase "sea power" and emphasized the importance of naval power for a nation's greatness.
Step-by-step explanation:
The person who coined the phrase "sea power" is Alfred Mahan. In his book "The Influence of Sea Power upon History, 1660-1783" published in 1890, Mahan argued that naval power was crucial for a nation's greatness. He emphasized the need for a strong navy, the establishment of military bases around the world, and the construction of a canal through Central America. Mahan's ideas greatly influenced policy makers and contributed to the expansion of the United States as a naval power.