Complex sentence: The Romans conquered the Western Iberian Peninsula, which they called Hispania: later part of the Roman provinces of Lusitania and Gallaecia, currently Portugal and Galicia (the northwestern region of Spain).
Split into simpler sentences: The Romans conquered the Iberian Peninsula, which they called Hispania. Western Hispania was then made up of Lusitania in the south and Gallaecia in the north, currently Portugal and Galicia (the northwestern region of Spain).