It is our faith that all that happened had the sanction of Allah and was in accordance with His Will. This is evident from the fact that during the caliphate of Abu Bakr and Umar, extensive conquests were made which changed the course of history. It was nothing short of a miracle that the Arabs of the desert overpowered the mighty kingdom of Persia in the east, and the empire of the Byzantines in the west. This would not have been possible if the blessings of God were not with the regime, which had come to be established after the death of the Holy Prophet. When God favored these Caliphs, it hardly lies in the mouth of anyone to say that they were usurpers.
"When a person dies, his works end, except for three: ongoing charity, knowledge that is benefited from, and a righteous child who prays for him."
Prophet Mohammed (PBUH)
"The best of what a man leaves behind are three: a righteous child who supplicates for him, ongoing charity the reward of which reaches him, and knowledge that is acted upon after him."
Sunan Ibn Mājah
"Every day two angels come down from Heaven and one of them says, 'O Allah! Compensate every person who spends in Your Cause,' and the other (angel) says, 'O Allah! Destroy every miser.'"
Sahih Bukhari