Alexandromir

What would have happened if the Dacian leader Decebal used the massive Dacian wealth to hire mercenary armies to fight Trajan's legions between the wars of 101-102 and 105-106 instead of hoarding it all? Or even before that? Clearly his overconfidence and underestimation of the power of the Romans was the main cause of their destruction.

Nick

Interesting idea. Dacia was advanced and wealthy before the Roman invasion. If they did a bit of their own empire-building, engaged in overseas trade and formed alliances with enemies of Rome like Parthia they could have preserved their independence. Or alternatively their actions may have provoked another war with Rome concerned by their power.

Julius Nepos

First, please, no fireworks.

Salah

Decebalus and his men probably would've ran amuck in the Moesiae and Pannoniae for a while, then withdrew with their booty. Things would continue much as before - the Dacians would raid Roman territory, but only destroy Roman armies when the latter entered Dacia. Some other bellicose emperor with time on his hands would've probably attempted to conquer them again.

If Trajan and his legions were completely annihilated - a sort of Adrianople three centuries early - perhaps Decebalus would permanently incorporate the Roman Balkans into his kingdom. This would probably be the beginning of decades of destructive warfare, and would possibly cause a terminal (if gradual) decline in Rome's power a few centuries early.

That's just my (far-fetched) take...

LordBlades

I really don't see the Dacians surviving as an independent entity for long, even with mercenaries.

It's pretty likely they would have repelled both Trajan's invasion attempts and this might have made the Romans consider that taking Dacia was not worth the resources.

But would the Dacians have stopped here? I doubt it. As shown under Burebista, the Dacian state had expansion ambitions, and they would have most likely ended up invading Roman land sooner or later (encouraged by their previous victories against Roman armies). This would have changed Dacia's position in the roman priority list from 'country we want to conquer' to 'country that's a threat to our empire'. I assume the Romans would be willing to put much more resources on the line in the latter case, and I honestly doubt the Dacians had the manpower and money to survive an all-out attrition war with Rome.

Of course, the attrition would have been mutual, and this, as Salah ad-Din said, would have probably accelerated the collapse of the Empire.

Perix

Probably, if Decebalus would succeded to defeat Trajan, the way to conquer all balkans would been wide open. But to create his own empire in the balkans is another question. south danube balkans were much more developed than dacian teritories, so, the ventual dacian empire core would had to move south Danube. The gold and silver of dacians would been not enough to deal with an empire, so, probably soon would been transformed into earlier east roman empire(if would been not defeated, by west part), with an ephemer dacian dinasty.
Anyway, the chances would been much higher if the Burebista would been not asasinated, and dacian centralised state would lasted. I think the death of Burebista was a real providential random for romans