WASHINGTON — The United States determined on Tuesday that members of Sudan’s Rapid Support Forces and allied militias committed genocide in Sudan and it imposed sanctions on the group’s leader over a conflict that has killed tens of thousands of people and driven millions from their homes. U.S. Secretary of State Antony Blinken said in a statement the RSF and aligned militias had continued to direct attacks against civilians, adding that they had systematically murdered men and boys on an ethnic basis and had deliberately targeted women and girls from certain ethnic groups for rape and other forms of sexual