Year 607
Ghassanid Lands
For decades, the Ghassanids had protected the southern flank against the Bedouin nomads of the Arabian Peninsula but also against their traditional rivals, the Lakhmids (clients of the Sasanian Empire). However, in 586 under the reign of Maurice, the Ghassanid Confederation had largely fallen apart into a mixed assortment of tribes and proved only partially capable of organized opposition to the Bedouin raiders passing through to assault Syria.
Finally irritated by the lack of protection by the Ghassanids, the Emperor in 606 called in reinforcements from an unexpected region: the Turkic peoples called the Bulgars, enemies of the Avars north of the Danube, dwelt north of the Black Sea. A pastoral nation, the Bulgars were expert horsemen something the Byzantines lacked in any great numbers. Too many people of the Byzantine Empire had become too "civilized", giving up the advantages of a swift army.
It was hoped that the Bulgars (lured by promises of plunder and lands rather than Byzantine coin) would be able to secure the frontier better than the Ghassanids. The early battles against southern raiders went well. Offering up large amounts of land in southern Syria as well as those in desolated Ghassanid and even some Bedouin territories, the Bulgars were told to be at home.
Of course, these arid regions were hardly hospitable, even to those used to the harsh northern Steppes. Still, the Bulgars took to the work. Unlike many armies, tens of thousands of women and children followed, effectively entire tribes on the move. Over 20,000 Bulgars had arrived in the southern lands by 607 and more would trickle in over the years, including some Turkic-peoples from the east.
It was feared that the Ghassanids would resist this migration. However, there was a rather different reaction. The Ghassanids had mostly practiced the "officially" heretical Miaphysite faith. This was an irritation to Byzantium and Rome but most Emperors were willing to ignore this out of convenience. If they couldn't get the Syrians and Egyptians to worship the proper faith, why bother with the Ghassanids?
As it was, a few thousand Ghassanids of various tribes were hired by the Byzantines to aid the Bulgars, Syrians and Egyptians in punishing some of the Bedouin tribes by attacking deep into their lands. As the only ones who knew the area, the Ghassinids were vital despite their weakness. However, within a few years, the faith of these Miaphysite peoples would soon start influencing the Bulgars. As more and more Turkic peoples migrated southward into northern Arabia, this would prove to be the preferred faith for converts from the native Turkic religion (Tengrism).
Lakhmid Lands
The Lakhmids had served a similar purpose to the Sasanian Empire as did the Ghassamids to the Byzantines. However, here the prevailing religion was Nestorianism (encouraged by the Sasanians in order to split the Christian faith).
As it happened, the Sasanian Empire had been followed the example of the Byzantines. Throughout the two previous years, the endless wars with the Gokturks (Western Turkic Khaganate) along the northern frontier had continued (and taken much of Khosrow II's attention). Many were surprised that he didn't take advantage of the weakened Byzantine position in the west but the Emperor, having already lost his throne once to usurpers, were more interested in strengthening his center of power. By what he saw in the west, the Byzantine was hardly going to be a threat in the near future. If necessary, they could be dealt with later.
As it was, the relationship between Khosrow and his client in the Lakhmid Kingdom, Al-Nu'man, deteriorated despite many years of good service.
Al-Nu'man quarreled with Sasanian diplomats even as he dealt internally with his own tribal rivalries. In 602, Khosrow II was ready to kill Al-Nu'man when yet another raid by from the eastern mountain people occurred. Knowing that Al-Nu'Man was not going to help much, the Khosrow looked north for help. Naturally, the Turks were not the answer. Usually, the Sasanians would attempt to divide and conquer the northern barbarians. However few tribes could challenge the Western Turkic Khaganate, which now ruled the steppes north of the Empire.
There was one group of people, though, who Khosrow thought he could hire. The Magyars spoke a northern Uralic language (that of the FAR north) betraying their origins and relations in northern Europe. For whatever reason, they'd migrated down from the mountains into the Turkic-dominated plains. A strong nation, the Magyars were hardly capable of tackling the Khaganate. However, as a horse-people, they would prove useful to the Sasanians. Tens of thousands of Magyars, including their families, would be called into the Sasanian Empire and dispatched to the east to battle the people of the mountains (including the Hephthalites who crushed the Persians in 603 after years of raiding).
The Magyars inflicted a terrible defeat upon the Hephthalites in 605 and spent much of 606 on a retribution campaign.
By the winter of 606, the Magyars had returned and Khosrow II realized that he didn't particularly WANT tens of thousands of these people in Persia. Thus he sent them southwards into Mesopotamia and then on to the Lakhmid Kingdom. Here Al-Nu'man would be informed of his new "allies" to be used against the Bedouin raiders also attacking the Lakhmids. Though he hardly wanted the "help", Al-Nu'man realized to refuse would probably result in the Sasanian Emperor attempting to exterminate him....again.
Thus, the Magyars would be put to use against the assorted northern Arab tribes.
Like the Bulgars in the Ghassanid lands, the Magyars would be exposed to Christianity, this time Nestorianism.
Note: Both of these maps are courtesy of wikipedia.