Complex sentence: First and Second Brigades of the Second Division, Second Army Corps were designated as the 3rd Division of the 5th Army Corps, but was later reassigned to the 2nd Army Corps.
Split into simpler sentences: First and Second Brigades of the Second Division, Second Army Corps were sent here. This Division was designated as the 3rd Division of the 5th Army Corps, but had been reassigned to the 2nd Army Corps.