分析:本句的主干是Washington…overcame the strong opposition…。Who引导的非限定性定语从句对先行词Washington做进一步的解释说明。该定语从句中,who代替Washington充当主语,谓语是had begun to believe,宾语是that引导的定语从句,after observing the bravery of the black soldiers during the Revolutionary War是这个定语从句的时间状语,说明“开始相信”的时间。主句中,of his relatives修饰的是前面的opposition,而to grant his slaves their freedom in his will表明了华盛顿不顾亲人反对也要实现的目的。