Complex sentence: In 1376 Olav inherited the crown of Denmark from his maternal grandfather as King Oluf III, with his mother as guardian; when Haakon VI died in 1380, Olav also inherited the crown of Norway.
Split into simpler sentences: In 1376 Olav inherited the crown of Denmark from his maternal grandfather as King Oluf III, with his mother as guardian. When Haakon VI died in 1380, Olav also inherited the crown of Norway.