Complex sentence: In 1961, part of the IX Corps was split into the 9th Regional Support Command, subordinate to the US Army Pacific command though the 9th Regional Support Command was an independent unit, it continued to operate closely with IX Corps.
Split into simpler sentences: In 1961, part of the IX Corps was split into the 9th Regional Support Command, subordinate to the US Army Pacific command. Though the 9th Regional Support Command was an independent unit, it continued to operate closely with IX Corps.