Complex sentence: Fire arrows of some type have been used in Japan as far back as the 6th century were they are said to have been used during a military campaign against Korea, bows (yumi) were used to launch these early fire arrows.
Split into simpler sentences: Fire arrows of some type have been used in Japan as far back as the 6th century where they are said to have been used during a military campaign in Korea. Bows (yumi) were used to launch these early fire arrows.