Complex sentence: In January 2009, the Saudi Arabian and Yemeni al-Qaeda branches merged to form Al-Qaeda in the Arabian Peninsula, which is based in Yemen, and many of its members were Saudi nationals who had been released from Guantanamo Bay.
Split into simpler sentences: In January 2009, the Saudi Arabian and Yemeni al-Qaeda branches merged to form Al-Qaeda in the Arabian Peninsula (AQAP). Al Qaeda in the Arabian Peninsula is based in Yemen, and many of its members were Saudi nationals who had been released from Guantanamo Bay.