Original: During his campaign against the Sassanid Persian Empire ( Iraq 633 - 634 ) and Byzantine Empire ( Syria 634 - 638 ) Khalid developed brilliant tactics , that he used effectively against both the Sassanid army and Byzantine army .
Simplified: During his campaign against the Persian Empire ( Iraq 633 - 634 ) and Byzantine Empire ( Syria 634 - 638 ) Khalid developed brilliant tactics .