While no one can predict where the next war will happen, one possible flashpoint between the U.S. and China is the Senkaku islands in the East China Sea.
The uninhabited islands are controlled by Japan but claimed by China, said Carl Baker, with the Center for Strategic and International Studies.
U.S. Marines on Okinawa have been helping the Japanese Self Defense Forces prepare for amphibious warfare in case they need to retake the islands from a Chinese invasion, said Baker, director of programs at Pacific Forum CSIS in Honolulu.
Chinese military aircraft and coast guard vessels have conducted patrols near the islands, inside what Japan considers to be its territory.
“I think there’s a real possibility that there could be a conflict of some sort over the Senkakus and the United States would feel very obliged to support the Japanese in protecting the Senkakus,” Baker said.
Other places where Marines might be called upon to fight include the Korean peninsula and the South China Sea, Baker said.
North Korea has made rapid progress recently on developing its own ballistic missiles and nuclear weapons. If North Korea invaded South Korea, Marines based in Okinawa could be used for an amphibious landing behind enemy lines.
Meanwhile, China continues to turn shoals and reefs in the South China Sea into man-made islands, where they have deployed aircraft, radar and other military equipment. The U.S. government maintains that the islands are in international waters, and in August the destroyer John S. McCain sailed within 12 nautical miles of Mischief Reef.
On the other side of the world, Marines could play a role in protecting Norway if Russia attacked a NATO member. About 300 Marines from Camp Lejeune, North Carolina recently began a training mission in Norway and the Marine Corps stores equipment in Norwegian caves to supply up to 15,000 Marines for a month.
“We shouldn’t see this small contingent of U.S. Marines in Norway as a deterrent in itself: It is simply providing a capability for rapid expansion, should it be necessary,” said Keir Giles, a Russia expert with the Chatham House policy institute in London.