Complex sentence: In the 1970s, 1900 elephants were killed in Kenya for their ivory tusks, increasing to 8300 elephants in the 1980s, but decreasing between 1990, when the 1990 CITES ban was issued, and 1997, when only 34 were illegally killed.
Split into simpler sentences: In the 1970s, 1900 elephants were killed in Kenya for their ivory tusks, increasing to 8300 elephants in the 1980s. Illegal elephant deaths decreased between 1990, when the 1990 CITES ban was issued, and 1997, when only 34 were illegally killed.