In 1281 during the Koan War of Genko (Mongol invasion attempts against Japan), Sadatsuna was ordered by Tokimune HOJO, the regent to the shogunate, to go down to the battle field of Kyushu.
弘安4年（1281年）の元寇の弘安の役では執権・北条時宗の命を受けて九州に出陣した。