Complex sentence: He helped to found the pro-independence United Gold Coast Convention; when Kwame Nkrumah returned from abroad, he took command of the UGCC and transformed it from a grassroots movement into a political party.
Split into simpler sentences: He helped to found the pro-independence United Gold Coast Convention. When Kwame Nkrumah returned from abroad, he took command of the UGCC and transformed it from a grassroots movement into a political party.