Complex sentence: At the time, April 29 was a national holiday for the birthday of Emperor Showa, but after his death in 1989, the day was renamed as "Greenery Day" in order to retain Golden Week.
Split into simpler sentences: At the time, April 29 was a national holiday celebrating the birth of Emperor Showa. Upon his death in 1989, the day was renamed as "Greenery Day" in order to retain Golden Week.