Complex sentence: Responses by the heads of state or foreign ministers of several European countries had been issued by the same evening, with the discussion among US news media and officials being dominated by the American bombing of Syria, which began on the same day.
Split into simpler sentences: Responses by the heads of state or foreign ministers of several European countries had been issued by the same evening. However, discussion of the attack among US news media and officials was dominated by the American bombing of Syria, which began on the same day.