Praise be to Allah that Mecca, Khyber, the Arabian Peninsula and Yemen were conquered during the Holy Prophet's lifetime. The magi of Hajar accepted subjugation by paying the jizyah (recompense). The same happened with some parts of Syria also. The emperor of Rome, Heraclius, and the king of Egypt sent presents. The King of Alexanderia, Maquqis, and the ruler of Oman also did the same thing and thus expressed their obedience. The king of Ethiopia, Ismaha, embraced Islam and his successors too sent presents to the Prophet's Court.
Thereafter, when Allah Most High called back His beloved prophet to His own presence, Siddiq-e-Akbar took charge of the caliphate. He strengthened the state of the Arabian Peninsula and made it independent. At the same time he sent a strong army under Saifullah Khalid bin Waleed's command to Fars (Persia) where it started a series of conquests. He uprooted the stalwart trees of infidelity and planted instead the plants of Islam everywhere. He dispatched the temerarious devotees of Islam under Hazrat Abu Obaidah bin al-Jarrah and other noble Companions to different monarchical countries. They pulled down the signs of the Cross there and raised the flag of Islam. An army of the crusaders of Islam was sent to Egypt under Hazrat Amr bin al-Aas's command. After the capture of Egypt, Damascus, Harran, etc. Siddiq-e Akbar also passed away.
Then, through divine inspiration, the reins of the Islamic power were given into the hands of a great stalwart like Hazrat Umar The truth is that there had never passed under the sky a period of such holy successors after any prophet. It is simply an exercise in futility to search for an example in the world of Hazrat Umar's inherent strength, virtuous character, perfect justness and fear of Allah. The whole country of Syria, the entire Egypt and the greater part of Persia (Iran) was conquered during his caliphate regime. The vast empire of Kisra broke up into pieces. Kisra himself could not find a place to hide therein; with utter helplessness and indignity he kept running from place to place. Caesar was also captured. His very name was obliterated. He had to give up the state of Syria and had to take shelter in Constantinople. The wealth and treasures of these empires, accumulated and amassed over the centuries, these slaves of Allah spent upon the pious and poor slaves of Allah and thus those promises Allah had made verbally with the Prophet were fulfilled.
Then comes the period of Hazrat Usman's caliphate and religion spreads to the far reaches of the east and the west. The Islamic army, on the one hand, reaches the eastern horizon and, on the other, goes to the extreme west and takes the rest. The belief of Divine Unity too accompanies the crusaders of Islam; while their bright swords conquer countries, this true belief conquers the hearts of those people who, disgusted with polytheism, were in search of the true doctrine. Andalusia (Spain), Cyprus, Qairwan, even lands up to China, were conquered during Hazrat Usman's time. A treacherous, greedy Persian brought Kisra (Yezdegird III) to his death. Fire-temples where fire had blazed for centuries non-stop cooled down and instead the sound of Allahu Akbar (Azaan-prayer-call) began to rise from every knoll and mound. On the other side, Ctesiphon (Mada'in), Khurasan and Ahwaz, all were captured. A Great War was fought with the Turks and their king, Khaqan, was put to disgrace. The warriors of Islam collected tributes from every nook and corner of the east and the west and sent it to the caliphate court. After Hazrat Usman's martyrdom begins Hazrat Ali's caliphate.