Some 28,500 US troops are based in South Korea and 47,000 in Japan. On the campaign trail, Trump raised the possibility of Japan and South Korea arming themselves with nuclear weapons, and accused Seoul and Tokyo of not paying their fair share for US troops stationed in their countries.
'The trip will underscore the commitment of the United States to our enduring alliances with Japan and the Republic of Korea (South Korea), and further strengthen US-Japan-Republic of Korea security cooperation,' the Pentagon said in a statement. The defense secretary's visit marks the first overseas trip of any senior official in the government of President Donald Trump, who suggested while campaigning that America's longstanding role in Northeast Asia could change. New Pentagon chief James Mattis on Wednesday heads to South Korea and Japan, where he will seek to reassure the key US allies about American security commitments in the region.