Complex sentence: Major General James G. Blunt, who commanded the District of South Kansas, was placed in command of the army's 1st Division, which was broken up into three brigade of volunteer cavalry regiments and a fourth of Kansas state militia units.
Split into simpler sentences: Major General James G. Blunt who commanded the District of South Kansas was placed in command of the army's first division. The 1st Division was broken up into 3 brigade of volunteer cavalry regiments and a fourth of Kansas state militia units.