Complex sentence: Ironically, Sun Yat-sen's new government was not based on the Provisional Constitution; rather, it was a military government and Sun was its "Grand Commander of the Armed Forces" (translated in the Western press as "Generalissimo").
Split into simpler sentences: Ironically, Sun Yat-sen's new government was not based on the Provisional Constitution. Rather, the new government was a military government and Sun was its "Grand Commander of the Armed Forces" (translated in the Western press as "Generalissimo").