Complex sentence: Holden's election as the first African-American Mayor-President of East Baton Rouge Parish was fostered through the support of his urban black base but also with substantial support from suburban white, many being Republicans.
Split into simpler sentences: Holden's election is significant in that he is the first African-American Mayor-President of East Baton Rouge Parish. His election was fostered through the support of his urban black base but also with substantial support from suburban white, many being Republicans.