Early Muslim Expansion — Khalid, Yarmouk, Al-Qadisiyyah Documentary
About 1400 years ago ,
In the East of Arab, Roman Republic (State)
In the West of the Arab, Persian (Parthian) Empire.
The Roman and Persian Empire were continuously at war on the entities that were at the border.
Then
Battle of Carrhae held :
The Battle of Carrhae was fought in 53 BC (60sBC) between the Roman Republic and the Parthian Empire near the ancient town of Carrhae (present-day Harran, Turkey).
After the war,
Roman state transitioned to Roman Empire
And the Parthian Empire to the Sassanid Empire…
Ghassanids and Lakhmids tribes migrated from Yemen to the borders of the Roman and Sassanid empire respectively ..Both these tribes were allies of respective empires and participated in many wars for their allies..
After a long time . Miaphysite(Christians of the Roman Empire) considered monophysite(Christians of Ghassanids ) to be heretical. Miaphysite attacked on them .Due to this the Ghassanids became against the Romans
And on the other side,
In the tribe of Lakhmids ;due to religious tensions the Sassanid empire started to fight with Lakhmid who were also supporters of the Sassanid empire. In 602AD, Shah Khusru ,King of Parthian Empire attacked them and executed Lakhmid king Al Nauman and captured Lakhmid and turned it into a province..
Lakhmids called for help from Arabs. Then allied forces from Arabs managed to defeat the Sassanid empire at Dhi Qar in 609AD….But Lakhmids always remained a province under the Sassanid empire .
In 602, Sassanid started a war with the Roman empire….Sassanid got impressive victories .
In 611 Hercules got the throne of the Roman empire. He tried to resist them but couldn’t..
By 621 the Sassanid empire marked the largest territory by continuous victories in different lands like Caucasus, Levant, Egypt, Anatolia etc.