Complex sentence: He remained commander till he resigned in March, 1864, due to quarrels with his commander, General Henry Wise, and in May of that year became Lieutenant Colonel and commander of the 1st Virginia Reserves Battalion.
Split into simpler sentences: He remained commander till he resigned in March, 1864, due to quarrels with his commander, General Henry Wise. In May, 1864, Duke became Lieutenant Colonel and commander of the 1st Virginia Reserves Battalion.