Complex sentence: In the past it was called'Namsan Tower', but is called'N Seoul Tower' today, though its proper name is'YTN Seoul Tower', because'YTN' (Korean broadcast center) took it over in 2000.
Split into simpler sentences: In the past it was called'Namsan Tower', nowadays it is called by'N Seoul Tower'. Actually its real name is'YTN Seoul Tower', because'YTN' (Korean broadcast center) was undertaked in 2000.