When Abu Bakr, may Allah be pleased with him, became the Caliph in 632 CE, the Islamic State was threatened with disunity and chaos. Within a year, Abu Bakr, may Allah be pleased with him, was strong enough to attack the Persian Empire in the north-east and the Byzantine Empire in the north-west. There were legitimate purposes for this conquest:

1- Along the borders between Arabia and these two great empires were numerous Arab tribes leading a nomadic life and forming a buffer-like state between the Persians and Romans. Abu Bakr, may Allah be pleased with him, hoped that these tribes might accept Islam and help their brethren in spreading it.

2- The Persian and Roman taxation laws were arbitrary and oppressive; Abu Bakr, may Allah be pleased with him, believed that they might be persuaded to help the Muslims, who sought to release them from injustice.

3- Two gigantic empires surrounded Arabia, and it was unsafe to remain passive with these two powers on its borders. Abu Bakr hoped that by attacking Iraq and Syria he might remove the danger from the borders of the Islamic State.

Conquest of the Persian Empire

We have mentioned that the Caliph Abu Bakr, may Allah be pleased with him,  sent Al-Ala’a bin Al-Hadhrami, may Allah be pleased with him, to subdue the renegade tribes in Bahrain on the Persian Gulf. The Bahraini leader, Muthannaa, helped Al-Hadhrami to subdue his own native apostates. Muthannaa, may Allah be pleased with him, did not feel that his contribution was enough, so he marched northwards along the coast of the Gulf until he reached the borders of `Iraq. In order to invade the Persian Empire he needed Abu Bakr's consent. Therefore, he traveled to Al-Madeenah where, after taking his counselors' advice, (particularly that of Khaalid bin Al-Waleed, may Allah be pleased with him) Abu Bakr, may Allah be pleased with him, officially appointed Muthannaa commander in the Arabian Gulf area.

No sooner had Muthannaa left Al-Madeenah than he was joined by Khaalid bin Al-Waleed, may Allah be pleased with him, at the head of a 10,000 strong army. When the two joined forces at the borders near the delta, Khaalid sent a letter to Hormuz, the Persian governor and leader, offering him three options: to embrace Islam, to pay tribute or to fight.

Hormuz was an intolerable man. He was disliked by the 'Iraqis who used to say of him: "There is no infidel more wicked than Hormuz." Yet, in Persia he was regarded as a nobleman of the highest rank.

Getting no reply, Khaalid divided his army into three regiments of 6,000 men each. The first day Muthannaa marched to Hafeer; the second day 'Adiyy bin Haatim, may Allah be pleased with him, followed; and the third day Khaalid found Hormuz occupying the water springs.

Hormuz wanted to cut the fight short by murdering Khaalid treacherously. As soon as the two armies engaged in battle, he challenged Khaalid to fight a duel. Khaalid at once dismounted and before long, his opponent was killed and Khaalid cut off his head and held it by the forelock. The Persians dashed up at full gallop to prevent their captain's death, but the Muslims were ready for them. The Persians took to their heels and a massacre followed. Among the spoils sent to Al-Madeenah were Hormuz's beret and an elephant. The huge animal was publicly admired by old and young, and then returned to 'Iraq to be made use of in the forthcoming campaign. This battle was called “The Battle of the Chains” and it was one of the most important battles, because of its effect on the morale of the Muslim troops. Muslim forces gave blow after blow to the Persian armies. Many places such as Al-Heerah, Al-Anbaar, 'Ayn At-Tamr, and Dawmat Al-Jandal surrendered to the Muslims.

Conquest of the Roman Empire

The marvellous victories of Khaalid bin Al-Waleed, may Allah be pleased with him, in `Iraq encouraged Abu Bakr, may Allah be pleased with him, to send armies to conquer Syria. Abu Bakr sent Khaalid bin Sa'eed, may Allah be pleased with him, at the head of an army to Tayma', just near the Syrian border, but he did not intend to invade the country; it was only a defensive measure. However, when he received letters from Khaalid bin Sa'eed, who longed for military glory in Syria as great as that of Khaalid bin Al-Waleed in `Iraq, asking for permission to proceed, he agreed and gave the signal which started a new campaign. In his first engagement with the Romans, Khaalid bin Sa'eed managed to win the battle and occupy the Roman camps. Tasting victory against "the people of yellow complexion", as they were usually described by the Arabs, Khaalid pushed forward till he reached the shores of the Dead Sea, where he defeated another Roman regiment near Qastal.

Now, the Romans realized that the Muslims were not merely indulging in temporary raids as they used to do before, but that they intended to conquer and stay. So, they sent a huge army led by Bahan, who was well known for his clever military tactics. He withdrew intentionally before Khaalid, who forgot Abu Bakr's piece of advice to be always wary in his war with the Romans. Bahan's retreat stopped when he was in the vicinity of Tiberias. There he managed to trap the Muslims and kill Khaalid's son, Sa'eed, who was lagging behind with a group of his men.

The Battle of Yarmook:

The circumstances, which befell Ibn Sa'eed, did not make Abu Bakr despair. He ordered the recruitment of new troops and immediately sent aid to 'Ikrimah, may Allah be pleased with him, who was waiting near the Roman border. The total aid which `Ikrimah received amounted to 30,000 men. `Amr bin Al-'Aas had to proceed to Palestine, Abu `Ubaydah bin Al-Jarraah to Damascus, Sharhabeel bin Hasnah to Jordan and Yazeed bin Abu Sufyaan to Basrah.

When Heraclius, the Roman emperor, heard the news, he mustered about 240,000 troops. Theodore, his brother, led the huge army and proceeded to Waqusah, some 40 miles to the south of Yarmook, a tributary of the Jordan. He camped beside the left bank of the river on a spacious plateau which was surrounded on three sides by high mountains.

Later, both armies were locked together in a fierce fight. Although the Muslim army was deficient in number, it was more than a match for the Romans in courage and vitality. Their enthusiasm was so high that even women plunged into the battlefield to prove their bravery as fighters for Islam. Abu Sufyaan encouraged the Muslim soldiers with martial cries. The brave Muslim warriors performed such deeds of valor that have never been witnessed before. From morning to evening swords and daggers, arrows and spears remained in action. Exhausted by the daylong operations and frustrated with failure after failure, the Romans lost heart and began to retreat till they had the mountains at their backs, while the Muslims kept advancing and pushing them back till they started to flee.

The morning sun rose with the message of Muslim victory and the Roman soldiers were nowhere to be seen. Theodore, the Roman commander and brother of Heraclius was killed along with a few other generals. An estimated 3000 Muslims were honored with martyrdom.

When Heraclius heard of his brother's defeat at Yarmook he left Homs, the imperial headquarters, and moved northwards. There he mustered a new army, which was met by the Muslims and defeated.

It was not long before Damascus opened two of its gates to the Muslims, one forced by Khaalid bin Al-Waleed, and the other opened peacefully by Abu `Ubaydah, may Allah be pleased with them. With the capital in the hands of the Muslims, and with the Romans driven out forever, Syria became an Islamic country.

The End

Abu Bakr, may Allah be pleased with him, died in the year 13 AH (634 AD) after suffering from fever for fifteen days during which he gave instructions that ‘Umar bin al-Khattaab, may Allah be pleased with him, should lead the prayers. During his suffering he was thinking of Islam and its future stability. After much meditation he decided to confer the Caliphate on ‘Umar bin al-Khattaab, may Allah be pleased with him. He consulted many of the well-known companions of the Prophet, (may Allah exalt his mention). Most of them approved of the choice, though they pointed out that ‘Umar bin al-Khattaab, may Allah be pleased with him, was rather rough. He called ’Uthmaan, may Allah be pleased with him, and put in writing his desire to choose ‘Umar as his successor. While he was dictating, he fainted but ‘Uthmaan completed the will on his own. When Abu Bakr, may Allah be pleased with him, recovered he was pleased with ‘Uthmaan's initiative and approved the will. Then he let it be read to the congregation, who accepted it and swore allegiance to ‘Umar, may Allah be pleased with him, in the Prophet’s Mosque. He watched what was going on from inside his house, being helped by his wife, Asmaa' bint 'Umays, may Allah be pleased with her.

Then he called ’Umar and advised him on how to lead his people, ending with these words: "If you follow my advice, nothing unknown will be more acceptable to you than death; but if you reject it, nothing unknown will be more frightening than death." Before he died, Abu Bakr, may Allah be pleased with him, gave back everything he had taken from the public treasury during his Caliphate. It is said that he did not bequeath any money at all. He left only a servant, a camel and a garment. His orders were that after his death the garment should be delivered to his successor. On seeing it ‘Umar wept and said: "Abu Bakr has made the task of his successor very difficult."

Sources:

The History of Islam, by: Akbar Shah Najeebadi