First of I am a history amateur, so this is more of a question rather than a statement. Half of my knowledge about how the frontier was handled comes from a single book "Empires and Barbarians" by Peter Heather, so not claiming much expertise.The West didn't seem to have much of a choice. In addition to the trouble with would-be and successful Roman usurpers, various Germanic nations were threatening the Empire's security from within and without. The ERE had its fair share of conflicts with barbarians and the Sassanids, but they had the wealth - and then some - to buy off their enemies for a time, whereas the West resorted to steps like giving away some of its own territories, which the barbarians used to essentially create states within a state; kingdoms within an empire. That could be a workable arrangement, but one of the downsides is that the more territory the West loses the less tax revenue it takes in.
Didn't both the western and eastern empire pay off the Germanic states for a long time? From my understanding the primary way both the west and east dealt with both their Rhine and Danubian frontiers was with money, making it very lucrative for the Germanic and later on Hunnic, Iranic and Slavic tribes to fight for the territory bordering the Roman Empire(s), thus weakening themselves. Divide and conquer, with only the occasional need to use expensive military force.
If so around what time did the western empire become unable to do so? Is it the damage done by Attila and civil war combined with the development of advanced more stable Germanic states, the eventual acceleration of the conglomeration of smaller Germanic groups into larger ones which would be harder to handle?
What I am asking is if, in your opinion, there was a specific turning point in history where the western Empire stopping being able to manipulate their frontier due to some event. Or if it was a combination of growing/advancing Germanic states and the west weakening internally over time? Was it primarily caused by the decline of the western empire or was it the growth and development of Central/Eastern Europe? Or were they both equally important in your opinion?
Why sail all the way to West Africa, which was dangerous for the Romans whom had limited ocean traveling capabilities, just to get slaves? They already got slaves and soldiers from Central and Eastern Europe, and it was much closer and easier to access. I can admit to gold in the Sahel being valuable, but not many really knew about the gold deposits in the area at the time, the first prominent state in the Sahel was the Kingdom of Ghana in 750AD~.Go and colonize West Africa. Idk if there are golds there... but just take natives as slaves and sell them to the East. Done
Also Western Rome "colonizing" Western Africa is not going to happen, too far away, hostile natives, tropical diseases and unfitting crops. Plus there was not a population surplus in the western empire. Also there was still plenty of land the settle and develop in Germania, Brittania, Northern Gallia, Western Hispania and to a lesser extent Eastern Hispania and Northern Gallia.
Keep in mind that the far more advanced European empires did not even attempt to make much progress into tropical Africa beyond coastal/river forts until vaccination and the Maxim Gun. It's simply "bad for the health" (understatement) for Europeans to settle in the tropics before vaccination is well developed.