The government will nationalize about 280 islands whose ownership is unknown out of the about 400 remote islands that serve as markers for determining Japan’s territorial waters, the state minister for oceanic policy and territorial issues has announced. Under the plan, announced Tuesday, the government will complete its search for the islands’ owners by June. Islands whose owners have not been tracked down by then will be registered on the national asset ledger. The move aims to clarify the government’s intention to protect territories and territorial waters by designating remote islands as “important national territories,” and to reinforce the management...