The Ghassanids، as the most important Christian Arab ally of the Byzantine Empire، played a decisive role in shaping the military and political equations of the western borders of Sassanid Iran. Although the two Ghassanid and Lakhmid states are often analyzed as buffer states، historical evidence shows that they were active agents in the defensive and offensive strategies of the two superpowers. This study، with a descriptive-analytical approach and relying on primary historical sources، examines the interactions of the Ghassanids with the Sassanids، Lakhmids، and Byzantium. Although the Ghassanids contributed to the erosion of the borders through proxy wars and tribal incitement، this process mainly made sense in the context of internal crises of the Sassanids (including the succession crisis، tax pressures، and Khosrow Parviz’s strategic mistake in dissolving the Lakhmids( The findings show that Byzantine military-political support for the Ghassanids strengthened their position against the Lakhmids to such an extent that the balance of power on the borders of Hira and the Levant shifted to the detriment of the Sassanids. The Ghassanids weakened the western borders of the Sassanids through mechanisms such as proxy and attrition wars، competition over trade routes، war with Hira، and intensification of insecurity and provocation of Arab tribes، and inflicting a heavy defeat on the Sassanids at Dhuqar. This process، with the occurrence of major internal problems for the Sassanid government، weakened the Sassanid defense and intelligence network and increased the influence and border attacks of the Byzantines and then the Arabs. The dissolution of the Lakhmid government in 602 AD، which was due to Khosrow Parviz's suspicion of Nu'man III، as a strategic self-defeat، deprived the Sassanids of an ally aware of the affairs of the Arab tribes.