The Pacific Ocean has three major North-South island chains, including the so-called “first island chain” that runs from the tip of the Kamchatka Peninsula down through the Kurile Islands, the Japanese home islands, Okinawa, Taiwan and on through to the Philippines. The so-called “second island chain” splits away from Japan, and runs southward toward the Bonins, Guam and the Marshall Islands. Meanwhile, the so-called “third island chain” runs from the end of the Aleutian Trench southward along the Emperor Seamount, through Midway, and ends up in the Hawaiian Islands (see Map 1).

During the late nineteenth century, Japan expanded along the first and second island chains and into the Western Pacific. In 1876, Japan obtained all of the Kurile Islands in exchange for ceding the southern half of Sakhalin Island to Russia, and also seized the Bonin Islands, about 1,300 kilometers to the southeast of Japan. In 1879, the Ryukyu Islands were formally annexed by Japan and became the prefecture of Okinawa. Finally, after the first Sino-Japanese War (1894–95), Japan obtained the island of Taiwan—in theory in perpetuity—in 1895, which gave it unbroken control from Kamchatka to Taiwan. Japan's expansion effectively cut the U.S. sea line of communication (SLOC) to China, which was considered to be a major trading partner.

In 1897, assistant secretary of the Navy, Theodore Roosevelt, and Commander C. J. Goodrich, president, U.S. Naval War College (NWC), carried on a confidential correspondence discussing how Japan's recent expansion impacted the United States. The original letters are in the NWC Historical Archives. On 23 June 1897, Goodrich explained that a Japanese attack on the United States would have to be staged from either Dutch Harbor (Unalaska) in the Aleutians or from Hawaii: