The Korean Peninsula, a strategically located feature critical to the defense of the Japanese archipelago, greatly occupied Japan's attention in the nineteenth century. Earlier tension over Korea had been settled temporarily through the Japan–Korea Treaty of 1876, which opened Korean ports to Japan, and through the Tianjin Convention in 1885, which provided for the removal from Korea of both Chinese and Japanese troops sent to support contending factions in the Korean court. In effect, the convention had made Korea a co-protectorate of Beijing and Tokyo at a time when Russian, British, and American interests in the peninsula also were on the increase.