Well Valens was killed and upto 35 high ranking officials, not to mention the core of the Eastern army. Massive effect on morale across the empire.
It's happened before; Sassanids used Valerian as the Shahanshah's personal slave, and Decius was killed by the Goths at Forum Terebronii. Besides, Theodosius (sort of) beat the Goths into submission after that. And there was no major barbarian incursion (excluding the brief attack by Uldin's Huns and Goths, which was smashed) until the West was invaded twenty-five years later by Radagaisus.
BCLG100 said:
The loss of so many men when the empire was already stretched meant that the Visigoths were free to do as they pleased as Rome no longer had the luxury of bouncing back,
But the men were lost in the
East; the West doesn't become overstretched because the Eastern Empire loses soldiers. And it wasn't actually that many men; less than 30,000 for the Romans IIRC, and in an army of hundreds of thousands when they
get a generation of peace to recover that's peanuts.
BCLG100 said:
instead they were forced into a position of having to use mercanerys.
1. The Romans always have used barbarian mercs as auxilia, even back in the time of the Republic; in addition, non-Roman troops, the
alae, made up at least half of all Roman field armies in times going back to the Kings. 2. The Romans didn't actually make up their losses with mercenaries; I cite the
Notitia Dignitatum, which instead refers to a transfer of forces from less threatened areas, like Egypt, to restore the field armies to full strength.
BCLG100 said:
He says if adrianopole had of been won, then the military reforms needed would have been called for and would have given the Romans time to regroup because that would have surely not been the end of the barbarians. They could have bounced back in a similar way to their decline in 188-284.
Military reforms
did occur (a defeat is always the best way of doing that). And I'm pretty sure that a generation of peace between Adrianople and the next major attack qualifies as "time to regroup". Victory at Adrianople means that the Goths are better assimilated in the Balkans, and maybe less of a necessity to transfer troops from less threatened theaters. Whoop-dee-doo. They would still have got hit by the avalanche of barbarian tribes in the first few decades of the fifth century, and the fact that the East is sitting relatively pretty
has no effect on the ability of the West to resist those invasions. Morale had nothing to do with it; this isn't the twentieth century, where Vietnam reverberates with the American public for decades. It's the fourth and fifth centuries, where most of the inhabitants of your empire don't hear anything about military victories or losses. Tactically, the Romans still had a massive advantage anyway, so long as they didn't do anything monumentally stupid. Radagaisus, with the largest invasion in the history of the Empire, got thrashed by Stilicho in northern Italy and chased out. So morale issues don't make any sense. It's the strategic problems of having to deal with the usual barbarians they know and love, except those barbarians have had the benefit of technological progress in the last few centuries, thus becoming very populous and better armed. Then the Huns start moving and kick off the avalanche.
BCLG100 said:
Ah but would the Schism have happened/been allowed to happen, by the time of the recorded date of the Great Schism it is highly likely the Roman empire would have a far more centralised and beuracratic state, probably inline with late seventeenth century european kingdoms.
What Great Schism?

There were always differences between the Eastern and Western Churches long before 1054, and they had several mini-schisms over the intervening centuries. Generally, the Bishop/Patriarch/Pope in Rome had fights with not only the "orthodox" officials in Constantinople and Antioch, but also with the monophysites in Alexandria and Jerusalem. So it'd be an interesting balancing act.