Japan along its western shore, Korea along its southern and eastern, and Russia along the eastern coast of its maritime province, are washed by the Sea of Japan. The communications between the sea and the Pacific Ocean are practically two only. One is on the north-east, namely, Tsugaru Strait; the other is on the south, namely, the channel between the extremity of the Korean peninsula and the Japanese island of the nine provinces. Tsugaru Strait is entirely under Japan's control. It is between her main island and her island of Yezo, and in case of need she can close it with mines. The channel between the southern extremity of Korea and Japan has a width of 102 m. and would therefore be a fine open sea-way were it free from islands. But almost mid-way in this channel lie the twin islands of Tsushima, and the space of 56 m. that separates them from Japan is narrowed by another island, Iki. Tsushima and Iki belong to the Japanese empire. The former has some exceptionally good harbours, constituting a naval base from which the channel on either side could easily be sealed. Thus the avenues from the Pacific Ocean to the Sea of Japan are controlled by the Japanese empire. In other words, access to the Pacific from Korea's eastern and southern coasts and access to the Pacific from Russia's maritime province depend upon Japan's goodwill. So far as Korea was concerned this question mattered little, it being her fate to depend upon the goodwill of Japan in affairs of much greater importance. But with Russia the case was different. Vladivostok, which until recent times was her principal port in the Far East, lies at the southern extremity of the maritime province; that is to say, on the north-western shore of the Japan Sea. It was therefore necessary for Russia that freedom of passage by the Tsushima channel should be secured, and to secure it one of two things was essential, namely, either that she herself should possess a fortified port on the Korean side, or that Japan should be bound neither to acquire such a port nor to impose any restriction upon the navigation of the strait. To put the matter briefly, Russia must either acquire a strong foothold for herself in southern Korea, or contrive that Japan should not acquire one. There was here a strong inducement for Russian aggression in Korea.