These are the world's most heavily contested seas

Countries in Conflict: Russia, Ukraine, and NATO

The Black Sea has become a point of geopolitical tension following Russia's annexation of the Crimean peninsula and the conflict with Ukraine. In June 2015, a Russian Su-24 buzzed a US guided-missile destroyer that was operating in the sea raising tensions between the two countries.

And earlier this month Ukraine and NATO member Turkey launched joint naval drills in the Black Sea as both countries face sharply deteriorating relations with Moscow.

Countries in Conflict: NATO and Russia

The Baltic Sea is ringed by NATO members, countries leaning towards NATO, and two Russian ports. Since Russia's annexation of the Crimean Peninsula and the start of the Ukraine crisis, tensions throughout the Baltics have steadily risen.

Most recently, on April 12, two Russian aircraft repeatedly flew simulated attack patterns over a US naval ship. In response to the incident, US Secretary of State John Kerry said that the US would have been in the right to shoot down one of the buzzing Russian aircraft — signalling the incredible tensions facing this part of the world.

Countries in Conflict: The international community and piracy

Located off of the Horn of Africa and Somalia, the Arabian Sea has had a history of being plagued by piracy. Tha Arabian Sea is connected to the Gulf of Oman and the Persian Gulf, both critical oil shipping routes.

However, thanks to a global patrol effort, piracy has continued to be on a steady decline in the Arabian Sea.

Countries in Conflict: Iran, the US, and the Arab Gulf nations

The Persian Gulf, which feeds into the Gulf of Oman and the Arabian Sea through the Strait of Hormuz, is one of the world's most critical waterways. Approximately 17 million barrels of oil, representing 30% of all maritime-traded petroleum, passed through the strait each day in 2013.

Due to the Persian Gulf's importance, Iran has indicated that it could be willing to disrupt the strait. Tehran has previously threatened to mine the waterway, and in February 2015 Iran carried out the destruction of a mock US aircraft carrier in the strait.

Countries in Conflict: China and Japan

China and Japan have had a steady and slowly simmering territorial conflict in the East China Sea over the Senkaku, or Diaoyu, Island chain. Although uninhabited, the islands sit atop of vast amount of estimated oil and natural gas. And China has slowly been trying to de facto take control of the region around the islands by increasing civilian fishing in the area.

Tensions in the region are likely to only increase further. At the end of March, Japan activated a new radar observation station in the East China Sea close to the disputed territory.

Countries in Conflict: Japan and Russia

The Sea of Okhotsk is a body of water separating northern Japan from Russia. Within the sea is the Kuril Island chain, which links Japan's northernmost island of Hokkaido with the Russian Kamchatka Peninsula. This island chain is in dispute, with Japan claiming that two of the Kuril Islands were seized by the Soviet Union following World War II and actually belong to Japan.

The issue of the Kurils have served as a snag in Russian-Japanese relations for decades. And, at the end of March, Russia announced intentions to deploy missiles and possibly construct naval bases on the Kuril Islands under its control, further militarizing the Sea of Okhotsk.

Countries in Conflict: China, The Philippines, Vietnam, Taiwan, and Malaysia

Over the past decade, China has pursued an extensive and far reaching campaign of dredging and creating man-made islands within the South China Sea. China has claimed virtually the entirety of the sea, and has moved missile systems and a military aircraft onto its man-made islands.

These pursuits have put China at odds with Vietnam, the Philippines, Taiwan, Malaysia, and large sections of the international community including the US. One of the main areas that China's expansion has focused on has been the Spratly Island chain close to the Philippines.