Complex sentence: As the 1960s progressed towards the 1970s, popular hairstyles--both within and outside of the black African-American community--became longer and longer; this resulted in an expansion in the overall size of Afros.
Split into simpler sentences: As the 1960s progressed towards the 1970s, popular hairstyles, both within and outside of the African-American community, became longer and longer. This resulted in an expansion in the overall size of Afros.