Complex sentence: Tokugawa Hidetada, on his way to join his father, Ieyasu, stopped to besiege Ueda Castle, which was held by Sanada Masayuki and his son Sanada Yukimura.
Split into simpler sentences: Tokugawa Hidetada, on his way to join his father, Ieyasu, stopped to siege Ueda Castle. The castle was held by Sanada Masayuki and his son Sanada Yukimura.