Abu Bakr planned his strategy accordingly. He divided the Muslim army into several corps. The strongest corps, and the primary force of the Muslims, was the corps of Khalid ibn al-Walid. This corps was used to fight the most powerful of the rebel forces. Other corps were given areas of secondary importance in which to bring the less dangerous apostate tribes to submission. Abu Bakr's plan was first to clear Najd and Western Arabia near Medina, then tackle Malik ibn Nuwayrah and his forces between the Najd and al-Bahrayn, and finally concentrate against the most dangerous enemy, Musaylimah and his allies in al-Yamama. After a series of successful campaigns Khalid ibn Walid defeated Musaylimah in the Battle of Yamama. The Campaign on the Apostasy was fought and completed during the eleventh year of the Hijri. The year 12 Hijri dawned on 18 March 633 with the Arabian peninsula united under the caliph in Medina.