Complex sentence: Armed groups inside Iraq have been increasingly galvanised by the Syrian Civil War, with Sunni factions standing against and Shia factions for the Assad regime, and numerous members of both sects have also crossed the border to fight in Syria.
Split into simpler sentences: Armed groups inside Iraq have been increasingly galvanised by the Syrian Civil War. Many Sunni factions stand against Assad regime, which Shia groups have moved to support, and numerous members of both sects have also crossed the border to fight in Syria.