The Philippine coast guard inaugurated a new monitoring base Friday on a remote island occupied by Filipino forces in the disputed South China Sea as Manila ramps up efforts to counter China’s increasingly aggressive actions in the strategic waterway. The high-seas faceoffs have fueled fears of a larger conflict that could involve the United States, which has repeatedly warned that it’s obligated to defend the Philippines, its oldest treaty ally in Asia, if Filipino forces, ships and aircraft come under an armed attack, including in the South China Sea. China has accused the U....