Complex sentence: On September 16,2004, the division headquarters finished its transformation, with 1st Brigade becoming the 1st Brigade Combat Team, and 3rd Brigade Combat Team, 10th Mountain Division was activated for the first time.
Split into simpler sentences: On September 16,2004, the division headquarters finished its transformation. The 1st Brigade became the 1st Brigade Combat Team, while the 3rd Brigade Combat Team, 10th Mountain Division was activated for the first time.