:salam2:
From A Book “Salah Ad-Din Al-Ayoobi” written by Dr. Ali Salabi. 
**The Byzantines
**
The origins of the Byzantine anti-Islamic movement go back to the time of the Messenger PBUH himself.
From the year 5 AH, in the battles of Doomat al-Jandal, Dhat as-Salasil, Mu’tah and Tabook, and ending with the campaign of Usamah ibn Zayd 
, the Byzantines realized the new danger coming from the south, especially after the emerging Islamic state managed to free a number of Arab tribes in the north of Arabia from their former Byzantine masters.
Whether the Byzantines were moving against Islamic forces on their own initiative or as a reaction against Muslim movements, the ultimate conclusion is that this state began to realize, more and more, the extent of the new challenge and began to prepare to stop it. It is true that on some occasions these preparations were not at the right level, which may have been due to lack of precise information on which the Byzantine leadership based its plans, but the outcome was that the fire of conflict broke out and intensified immediately after the death of the Prophet PUBH and after Islamic forces started pouring into the lands under Byzantine control.
The Byzantines were expelled from their possessions in Asia and parts of Africa at the hands of the Rightly Guided Caliphs.
During the subsequent period, which witnessed many attacks and counterattacks carried out by the Byzantines on land and sea, most of which ended in failure, the Byzantines soon retreated as a result of the persistent pursuit of the Umayyads, starting with Mu’awiyah, the founder of the Umayyad state, and the era of 'Abd al-Malik ibn Marwan and his sons, especially al-Waleed and Sulayman.
This active pursuit of the Byzantines continued after the Umayyad era, in Syria, Egypt and North Africa. They withdrew completely from North Africa and vast areas of the Mediterranean, and were confined to Anatolia and their possessions in Europe itself. With the passage of time, the danger of counterattacks grew less, because they were concentrated along a line stretching across Anatolia and the Euphrates Valley, rarely able to penetrate any deeper due to the alertness of the Islamic leadership, who fortified the borders and also launched ongoing attacks against the Byzantine state, penetrating deep in the direction of Constantinople itself.
This did not leave the Byzantine Emperor, in most cases, any room to broaden the scope of his counterattacks, except at the beginning of the fourth century AH, when the Abbasid state had grown weak.
The emergence of the Seljuks then gave a new impetus to the Islamic Jihad movement; during the reign of the Seljuk sultan Alp Arslan they were able to inflict a crushing blow to the backbone of the Byzantine forces in the battle of Manzikert (463 AH).
That victory spelled the end of the challenge posed by the Byzantine state and its counterattacks, and it remained ineffectual until it fell, many centuries later, to the Ottomans.
