There were many other barbarian “tribes” milling around the Empire’s borders, but of those who (by conventional understanding) initially set up kingdoms in the old Roman Empire in the West, all of them were forces within the Empire that worked with the Empire, in the context of perpetuating the Empire, just like the Franks, Vandals, and Goths.
The Anchor Atlas of World History (1974) shows the following “German states” in the areas that comprised the western portion of Roman Empire at its height, under Trajan: “Kingdom of the Suevi,” “Visigothic Kingdom,” “Burgundian Kingdom,” “Kingdom of Syagrius,” “Kingdom of the Franks,” “Vandal Kingdom,” “Odovacar’s Kingdom,” “Alamanni,” “Ostrogothic Kingdom.” That’s as of 486 AD. The map for 526 AD doesn’t show Syagrius or Odovacer, and it adds “Anglo-Saxons” to southern Britain.
Every one of these barbarian peoples (or individuals, in the case of Odovacer and Syagrius) operated within the context of the Empire, not against the Empire, with the possible exception of the Anglo-Saxons, and the record there is so muddled, I doubt anyone will ever determine anything with certainty (if you’ve looked into the King Arthur legends, you know what I’m talking about).
I also cannot with certainty state that the Alamanni ever worked within the context of being part of the Empire, but it’s intriguing that the Anchor Atlas merely refers to “Alamanni” (not the “Kingdom of the Alamanni”) and doesn’t even mention the Alamanni in the accompanying text, thereby supporting the notion that the barbarian “kingdoms” in the post-476 western Roman Empire were merely hubs of Roman rule, not “kingdoms” like we think of them today. The “kingdom” was merely a geographic area with a barbarian general (rex) within the Roman army (or his descendants) at its head, who worked with the local Roman aristocracy (descendants, often, of the Senatorial class), to keep the Roman Empire in the West going, albeit it in fractured form. If there were no Roman general at the head (as appears to be the case with the Alamanni, since I haven’t seen anything to indicate that the Alamanni worked within the context of the Empire), there was no “kingdom,” as tortured historical renditions like the Anchor Atlas of World History portray it.
Now contrast and compare all of the foregoing with Belloc’s description of what “barbarian king” really meant. He is writing about kings in the post-476 Roman West in Europe and the Faith:
“(1) The chieftain of an auxiliary group of soldiers who holds an Imperial commission: and it means (2) That man acting as a local governor. Centuries and centuries before, indeed a thousand years before, the word Rex had meant the chieftain of the little town and petty surrounding district of Rome or of some similar neighboring and small state. It had in the Latin language always retained some such connotation. The word ‘Rex’ was often used in Latin literature as we use the word ‘King’ in English: i.e., to describe the head of a state great or small. But as applied to the local rulers of the fifth century in Western Europe, it was not so used. It meant, as I have said, Chieftain or Chief officer of auxiliaries. A Rex was not then, in Spain, or in Gaul, a King in our modern sense of the word: he was only the military head of a particular armed force. He was originally the commander (hereditary or chosen or nominated by the Emperor) of an auxiliary force serving as part of the Roman Army. Later, when these troops—originally recruited perhaps from some one barbaric district—changed by slow degrees into a body half police, half noble, their original name would extend to the whole local army. The “Rex” of, say, Batavian auxiliaries, the commander of the Batavian Corps, would probably be a man of Batavian blood, with hereditary position and would be called ‘Rex Bataviorum.’ Afterwards, when the recruiting was mixed, he still kept that title and later still, when the Batavii, as such, had disappeared, his fixed title would remain. There was no similarity possible between the word Rex and the word Imperator, any more than there is between the words ‘Miners’ Union’ or ‘Trade Conference’ and the word ‘England.’ There was, of course, no sort of equality. A Roman General in the early part of the process planning a battle would think of a Rex as we think of a Divisionary General. He might say: ‘I shall put my regulars here in the centre. My auxiliaries (Huns or Goths or Franks or what not) I shall put here. Send for their ‘Rex’ and I will give him his orders.’”
I respectfully submit that, once again, Belloc’s description comes far closer to what was actually occurring than conventional textbook accounts. It certainly matches up much (much) closer to the historical reality of Theodosius’ armies painted by Duncan and Durant than the common notion that barbarian tribes were invading and migrating into the Roman Empire against the Empire’s will. That simply didn’t happen often, and when it did, the unwelcome invaders/immigrants were crushed.