HIROSHIMA, Japan —On the 75th anniversary of the atomic bombing of his city, the mayor of Hiroshima planned to warn the world about the rise of “self-centered nationalism” and appeal for greater international cooperation to overcome the coronavirus pandemic. Thursday morning in Hiroshima’s Peace Memorial Park — near the center of the Aug. 6, 1945, blast that destroyed the city — Kazumi Matsui was set to renew a “Peace Declaration” on behalf of the city and appeal to Japan’s government to ratify a 2017 U.N. treaty proposing the elimination of nuclear weapons, he told a news conference last week.