Complex sentence: Wendell Willkie, former Republican Presidential candidate, spoke at the NAACP convention, advocated an end to colonialism, and castigated white Americans for their attitude to African-Americans.
Split into simpler sentences: Wendell Willkie, former Republican Presidential candidate, spoke as part of the NAACP convention. Wilkie advocated an end to colonialism, and castigated white American for their attitude to African-Americans.