Complex sentence: In 1848, Pius IX ordered the demolition of the walls, which because of the resistance of the Romans had to be accomplished during the night, but was only after September 20,1870, that the Roman Jews ceased to be second class citizens.
Split into simpler sentences: In 1848, Pius IX ordered the demolition of the walls but, because of the resistance of the Romans, the task had to be accomplished during the night. Anyway, it was only after September 20,1870, that the Roman Jews ceased to be considered as second class citizens.