 Damascus fall in September 634 and Emesa fall in March 635.In the years 635, Emperor Heraclius successfully allied with Sassanid Persian Emperor Yazdegerd III on Yazdegerd III's request to crush the Muslim power.A well coordinated plan was agreed to launch a massive counterattack against Muslims in Iraq and Syria at once so that Muslims, because of the resulted pressure may retreat back to Arabia where they may be dealt in detail later, either by invading it or by economical and trade blockage.