Complex sentence: The kibbutzim held off the attacks for ten days until Kfar Etzion fell and was subject to what became known as the Kfar Etzion massacre on May 14, in which all but four of the defenders were summarily executed by Arab Legion and irregular forces.
Split into simpler sentences: The kibbutzim held off the attacks for ten days until Kfar Etzion fell. In the Kfar Etzion massacre on May 14, all but four of the inhabitants were executed by Arab Legion and irregular forces.