Complex sentence: Juiz de Fora is the second most important industrial center in the state, despite being only the fourth largest city in population, after having been the biggest city of the state at the beginning of the 20th century and holding the second position until the 1990s.
Split into simpler sentences: Juiz de Fora is the second most important industrial center in the state, despite being only the fourth largest city in population. It was the biggest city in the state at the beginning of the 20th century and held the second position until the 1990s.