BANGKOK, Thailand—The United States will help Thailand develop nuclear power through a new class of small reactors, part of a program aimed at fighting climate change, Vice President Kamala Harris announced on a visit Saturday. The White House said the assistance was part of its Net Zero World Initiative, a project launched at last year’s Glasgow climate summit in which the United States partners with the private sector and philanthropists to promote clean energy. Thailand does not have nuclear power, with the public mood on the issue souring after the 2011 Fukushima disaster in Japan. The White House said it...