Complex sentence: Dr. Washington, who had gained the respect of many American leaders as well as obtain financial support from wealthy philanthropists such as Henry Huttleston Rogers, encouraged Rosenwald, as he had others, to address the poor state of African American education in the US.
Split into simpler sentences: Dr. Washington, who had gained the respect of many American leaders, had also obtained financial support from wealthy philanthropists such as Henry Huttleston Rogers. He encouraged Rosenwald, as he had others, to address the poor state of African American education in the US.