Complex sentence: Israel's mobilised a force of around 3,000-4,000 soldiers, backed by tanks and aircraft, divided into a reserve force, which remained on the Israeli side of the border, and two raiding parties, which crossed into the Jordanian-occupied West Bank.
Split into simpler sentences: Israel's mobilised a force of around 3,000-4,000 soldiers, backed by tanks and aircraft. The force was divided into a large reserve force, which remained on the Israeli side of the border, and two attack forces, which crossed into the Jordanian-occupied West Bank.