Complex sentence: In the 1950s and 1960s the World Health Organization (WHO) disease was nearly eradicated, but since then the number of cases has increased and WHO is again trying eliminate the disease by 2020.
Split into simpler sentences: In the 1950s and 1960s the World Health Organization (WHO) disease nearly got rid of the disease. Since then the number of cases has increased and WHO is again trying get rid of the disease by 2020.