There are many indications of close relations between Kent and the Franks.
Æthelberht's marriage to Bertha certainly connected the two courts, although not as equals: the Franks would have thought of Æthelberht as an under-king.
There is no record that Æthelberht ever accepted a continental king as his overlord and, as a result, historians are divided on the true nature of the relationship.
Evidence for an explicit Frankish overlordship of Kent comes from a letter written by Pope Gregory the Great to Theuderic, king of Burgundy, and Theudebert, king of Austrasia.
The letter concerned Augustine's mission to Kent in 597, and in it Gregory says that he believes "that you wish your subjects in every respect to be converted to that faith in which you, their kings and lords, stand".
It may be that this is a papal compliment, rather than a description of the relationship between the kingdoms.
It also has been suggested that Liudhard, Bertha's chaplain, was intended as a representative of the Frankish church in Kent, which also could be interpreted as evidence of overlordship.

A possible reason for the willingness of the Franks to connect themselves with the Kentish court is the fact that a Frankish king, Chilperic I, is recorded as having conquered a people known as the Euthiones during the mid-sixth century.
If, as seems likely from the name, these people were the continental remnants of the Jutish invaders of Kent, then it may be that the marriage was intended as a unifying political move, reconnecting different branches of the same people.
Another perspective on the marriage may be gained by considering that it is likely that Æthelberht was not yet king at the time he and Bertha were wed: it may be that Frankish support for him, acquired via the marriage, was instrumental in gaining the throne for him.

Regardless of the political relationship between Æthelberht and the Franks, there is abundant evidence of strong connections across the English Channel.
There was a luxury trade between Kent and the Franks, and burial artefacts found include clothing, drink, and weapons that reflect Frankish cultural influence.
The Kentish burials have a greater range of imported goods than those of the neighbouring Anglo-Saxon regions, which is not surprising given Kent's easier access to trade across the English Channel.
In addition, the grave goods are both richer and more numerous in Kentish graves, implying that material wealth was derived from that trade.
Frankish influences also may be detected in the social and agrarian organization of Kent.
Other cultural influences may be seen in the burials as well, so it is not necessary to presume that there was direct settlement by the Franks in Kent.
There are many indications of close relations between Kent and the Franks. Æthelberht's marriage to Bertha certainly connected the two courts, although not as equals: the Franks would have thought of Æthelberht as an under-king. There is no record that Æthelberht ever accepted a continental king as his overlord and, as a result, historians are divided on the true nature of the relationship. Evidence for an explicit Frankish overlordship of Kent comes from a letter written by Pope Gregory the Great to Theuderic, king of Burgundy, and Theudebert, king of Austrasia. The letter concerned Augustine's mission to Kent in 597, and in it Gregory says that he believes "that you wish your subjects in every respect to be converted to that faith in which you, their kings and lords, stand". It may be that this is a papal compliment, rather than a description of the relationship between the kingdoms. It also has been suggested that Liudhard, Bertha's chaplain, was intended as a representative of the Frankish church in Kent, which also could be interpreted as evidence of overlordship.
A possible reason for the willingness of the Franks to connect themselves with the Kentish court is the fact that a Frankish king, Chilperic I, is recorded as having conquered a people known as the Euthiones during the mid-sixth century. If, as seems likely from the name, these people were the continental remnants of the Jutish invaders of Kent, then it may be that the marriage was intended as a unifying political move, reconnecting different branches of the same people. Another perspective on the marriage may be gained by considering that it is likely that Æthelberht was not yet king at the time he and Bertha were wed: it may be that Frankish support for him, acquired via the marriage, was instrumental in gaining the throne for him.
Regardless of the political relationship between Æthelberht and the Franks, there is abundant evidence of strong connections across the English Channel. There was a luxury trade between Kent and the Franks, and burial artefacts found include clothing, drink, and weapons that reflect Frankish cultural influence. The Kentish burials have a greater range of imported goods than those of the neighbouring Anglo-Saxon regions, which is not surprising given Kent's easier access to trade across the English Channel. In addition, the grave goods are both richer and more numerous in Kentish graves, implying that material wealth was derived from that trade. Frankish influences also may be detected in the social and agrarian organization of Kent. Other cultural influences may be seen in the burials as well, so it is not necessary to presume that there was direct settlement by the Franks in Kent.
Æthelberht of Kent