Complex sentence: Massive unemployment hit the mining town of Ojos Negros after mining activity in the nearby mountains ceased, therefore its population went from 3000 in the 20th century to 560 in 2010.
Split into simpler sentences: Massive unemployment hit the mining town of Ojos Negros after mining activity in the nearby mountains ceased. As a consequence its population went from 3000 in the 20th century to 560 in 2010.