When did the Roman Empire fall (your thoughts)?

[Robert Vermaat]

All too often federates were backstabbers. The Vandals got "federate" status in the treaty of 435 but a few years later they took Carthage.

One occasion does hardly makes this an 'all too often' practise, does it?

IIRC in 409 Honorius sought to hire 10,000 Huns, and Roman victories in Spain several years later were the work of hired barbarians.

So how is this proof for your statement that "By or after 408, the only way to fight one barbarian group was to hire another"? Honorius needed forces loyal to his person in a time of crisis, and the situation in Spain is not easy to analyse due to a dour lack of sources. Some modern authors think that no Roman troops were present after Constantine III! Anyway, which troops were hired barbarians there? Instead of federates I mean?