Complex sentence: Iraq met them with a mechanized division that slaughtered the Iranians but the Iranians simply were too large in numbers and the Iraqis although they were well equipped and enjoyed air support could not stop them.
Split into simpler sentences: Iraq met them with a mechanized division that slaughtered the Iranians. However, the Iranian force was too large and the Iraqis, although they were well equipped and enjoyed air support, could not stop them.