Defense Secretary Pete Hegseth has fired or sidelined at least two dozen generals and admirals over the past nine months in a series of ousters that could reshape the U.S. military for years to come. His actions, which are without precedent in recent decades, have come with little explanation. In many cases, they have run counter to the advice of top military leaders who fought alongside the officers in combat, senior military officials said. The utter unpredictability of Mr. Hegseth’s moves, as described in interviews with 20 current and former military officials, has created an atmosphere of anxiety and mistrust...