The Islands of Diaoyutai were discovered by the Chinese, but by the end of the XIX century at the end of first Sino-Japanese war the islands retreated to Japan. However, some time later, after the defeat of Germany and Japan in the Second world war, Japan lost the right to the conquered territories. These Islands have come under the jurisdiction of the United States. In the 70-ies of the last century, Washington returned to Japan Okinawa island with the Senkaku archipelago. The territorial conflict between China and Japan escalated in September 2012. Then Tokyo announced the procedure of nationalization of the Islands through their acquisition from private owners. This fact caused a sharp protest of China, across the country there was a wave of anti-Japanese demonstrations. Since then, China has regularly sent its own patrol ships to the disputed territories, thereby causing resentment in Japan.
It should be noted that the United States too added fuel to the fire. The United States is a fierce opponent of China's emerging dominance. They are trying by all means to reduce the power of China, and the territorial conflict is a good reason for this. If earlier relations between Japan and China were mainly limited to mutual accusations, then with the advent of the Americans began rattling weapons. Japan and the United States are developing a joint action plan to repel a potential Chinese attack on disputed territories in the East China sea.
Moreover, on February 3, 2017, the United States confirmed that the Senkaku Islands fall under the fifth article of the Treaty on mutual cooperation and security guarantees of 1960 between the United States and Japan. According to the fifth article of this document, each party regards any military aggression against an ally as a threat to its national security and has the right to act in this regard in accordance with the provisions of its own Constitution. This was stated by the Japanese foreign Minister Fumio Kishida following a meeting in Tokyo with the head of the Pentagon James Mattis. Earlier, Mattis held a meeting with Japanese Prime Minister Shinzo Abe, at which he noted that "the security Treaty between Japan and the United States is extremely important," especially in conditions when both countries face various challenges, such as the nuclear and missile programs of the DPRK. In addition, Mattis said that the US is ready to use nuclear weapons to protect Japan.
And on February 14, Japanese Prime Minister Shinzo Abe stated that during the recent negotiations with US President Donald Trump achieved his goals, as the head of the White house for the first time in writing made a commitment to protect the Tokyo-controlled Senkaku Islands, claimed by the people's Republic of China.
Japan and the United States are already developing a plan for the response of its armed forces in the event of a threat from the PRC, according to the Kyodo news agancy. The parties are consulting on this issue, and the final document is planned to be scheduled for March 2019. It is expected to spell out the actions of the Japanese self-defense forces and us troops in situations with which the Japanese coast guard is not able to cope on their own.