WASHINGTON -- The U.S. military capabilities allotted to the region illustrate that the Indo-Pacific is the focus of the U.S. military's main effort, the chairman of the Joint Chiefs of Staff said in Tokyo.Army Gen. Mark A. Milley spoke today to Japanese and American reporters at the conclusion of a meeting he had with Japanese leaders.Milley noted that the National Defense Strategy puts the Indo-Pacific region front and center. The region is home to the four most populous countries in the world: China, India, the United States and Indonesia, and it has the largest military forces in the world. The return of great power competition as a threat to the United States is played out in the Pacific, with China and Russia both trying to change the rules-based international order that has served the region so well.''It is the No. 1 regional priority for the United States military,'' Milley said.The United States is a global power, he said, capable of doing more than one thing at a time. In Europe, the United States counts on the NATO alliance to help guard American interests, Milley said. In the Pacific, the bilateral treaty allies -- Japan, South Korea, the Philippines, Thailand, Australia and New Zealand -- are the bedrock for U.S. diplomatic, economic, political and military efforts, he added.The purpose of U.S. efforts in Europe and Asia is to maintain peace and security, the chairman said. ''The bumper sticker for Indo-Pacific is 'a free and open Indo-Pacific,''' Milley said. ''That has been a U.S. policy … in one way or another for well over a century.''All of the nations of the region have benefitted from the rules-based international order since it was put in place at the end of World War II, he said, and the U.S. Indo-Pacific Command is the military component of the policy.U.S. Central Command is much in the news today for its fight violent extremist organization terrorist organizations and its dealing to deter Iran -- a regional malign actor. But with more than 300,000 service members and Defense Department civilians, U.S. Indo-Pacific Command dwarfs Centcom, the chairman said. The U.S. Pacific Air Forces alone is the second largest air force in the world. By itself, the U.S. Pacific Fleet would be the largest Navy in the world. The Army has a division in Hawaii and another in South Korea, as well as a significant presence in Alaska, the general said.''We've got a Marine division forward-based west of the [international date line] in Okinawa,'' he said. ''There is no other region in the world that has the amount, the capacity and the ... military capability like we do in the Indo-Pacific.''Great power competition in part of the calculus with China in the Indo-Pacific region. ''We need to continue to engage with China,'' the general said. ''China is a strategic competitor to be sure, [but] it doesn't necessarily mean that China becomes an adversary in the military sense of the word, or an enemy.''But having said that, it's important that the United States, Japan, South Korea, Australia, and other friends and allies in the region remain unified,'' the chairman continued. ''We have a common set of values, and we have a common set of national security interests.''China is building a very capable military, Milley said. ''They've had extraordinary growth and wealth over the last 40 years,'' he added. ''And following that growth and wealth is an increased military capability that they undoubtedly are demonstrating that they're willing to use in a variety of ways throughout the region.''China is trying to assert sovereignty over the South China Sea, he said. ''They've got a wide variety of other activities that they've been undertaking throughout the region that cause nations within the region to have concern about Chinese intentions going forward,'' the chairman said.The United States is not the only nation in the region worried by Chinese activities, Milley noted. Japan, South Korea, Australia and others have expressed concerns on the international stage, he said, and they must work together to maintain regional balances. ''We are committed to a free and open Indo-Pacific region, and will maintain very, very close security ties with our partner nations in the area,'' he said.The U.S. alliance with Japan is ''rock solid,'' the chairman said, and Japanese and American service members are very close. ''We train together. We have interoperable standards. We do a wide variety of exercises. We have engagements and meetings. We have similar standard operating procedures,'' the general said.The Japan Self-Defense Force and the U.S. military work together in all areas of warfare, including space and cyber -- the two newest domains.The U.S. has about 56,000 service members based in Japan, and those forces aid in the defense of the nation. ''We are committed to the mutual defense of both our countries' national interests in East Asia,'' Milley said.The position in Japan serves both countries well, defense officials have said. The U.S. has the capability to project power overseas from the continental United States, they've noted, but it is much more effective and efficient to be closer to the scene. Troops forward-deployed in Asia are more easily deployed and sustained.''So, for our ships and planes and troops to operate in any region of the world, it very, very much helps to have bases and overflight rights and have friends and allies in the region that can facilitate U.S. military operations,'' Milley said.One of the challenges with forward-basing U.S. forces is readiness, he said, due to restrictions on the available types of training. The general said he broached the subject with his Japanese counterparts during this visit.''I would also say that constraints and restraints on military training [are] not unique to Japan,'' he noted. ''It exists in Korea, it exists in Germany, it exists in the continental United States. Things like environmental issues, issues with the neighboring communities and towns of various military bases.''The U.S. military goes to great lengths to be good neighbors and to abide by local customs and rules to the extent possible while maintaining the required level of tactical and operational readiness, Milley said.The general is also working to save the bilateral agreement between Japan and South Korea called the General Security of Military Information Agreement. That agreement allows the two nations to quickly share information and intelligence, but disagreements on an unrelated issue mean it may expire Nov. 22.''The only ones who benefit from that … agreement expiring … is Pyongyang, and Beijing,'' he said. ''It's in China's strategic interest, it's in North Korea's strategic interest, to drive a wedge between South Korea and Japan, and South Korea, the United States and Japan. It's in everybody's interest -- … South Korea, Japan and the United States -- to ensure that that agreement does not expire, and that'll be my message to South Korea.''