As you can read at the following Reuters article, titled “Japan protests Russian PM’s visit to disputed island”, August 2015, the Kuriles Islands in the Sea of Okhotsk have strained relations between Japan and Russia since the end of World War 2. Russia calls the islands South Kuriles, and Japan calls them Northern Territories. Russia took control of the islands in the last days of World War 2. Russia was with the winners and Japan was with the losers of the war. You can see the disputed islands at the following map.
As you can see at the following map of Energy Information Administration, Russia produces 4% of her oil and 4% of her natural gas from the region near the Kuriles Islands, and Japan is a country very poor in energy resources. That problem became more important for Japan after the nuclear accident of Fukushima in 2011.
At the other end of Japan, at the East China Sea, Japan and China are facing each other over the Senkaku Islands, which are controlled by Japan, but Japanese control is disputed by China and Taiwan. See map 3 from Wikipedia.
Sea also map 4.
It is believed that the East China Sea is rich in resources, and as you can read at the following Reuters article, titled “Japan demands China halt oil exploration in part of East China Sea, July 2015, China is exploring the waters of East China Sea for oil , and Japan demands that China halts these operations.
Moreover Japan wants to prevent China from militarizing the islets of the South China Sea, which would make the South China Sea a Chinese lake. China claims control of almost the whole of the South China Sea, due to historical reasons, something strongly opposed by Vietnam, the Philippines, Malaysia, Indonesia and Taiwan, which are the other countries of the South China Sea. These countries are backed by India, Australia, Japan, South Korea, and of course by the US. See map 4.
The Straits of Malacca in South China Sea is one of the most important energy choke points of the world, second only to the Straits of Hormuz in the Persian Gulf, as you can see at the following table from the Energy Information Administration.
As you can see from the table, in 2013 17 million barrels of oil were passing daily from the Strait of Hormuz, and 15 million were passing from the Malacca Straits. At the following map you can see the most important energy choke points of the world.
You can see that Russia and China have a motive to cooperate against the US and their allies in the South China Sea, the East China Sea and the Sea of Okhtsok.
At the following article from the Financial Times, titled “Chinese boats fish in dangerous waters”, April 2012, you can read about China’s claims over the South China Sea. The following map is from the same FT article, and it depicts China’s claims. The Chinese “nine-dashed line” map.
For the conflict of the South China Sea see also Huffington Post, titled “Indonesia, America and China’s Nine-Dash Line”, August 2014.
Huffington Post, titled “U.S. Alliances Encourage Asian Allies to Be More Antagonistic Toward China”, May 2014.
Financial Times, titled “Construction on the high seas adds to Asian maritime tensions”, March 2015.
For the Reuters article about Japan and Russia see
“Japan protests Russian PM’s visit to disputed island”, August 2015
For the Reuters article about Japan and China see
“Japan demands China halt oil exploration in part of East China Sea, July 2015
For the Financial Times article about China and her claims in the South China Sea see
“Chinese boats fish in dangerous waters”, April 2012