I’ve been unintentionally focused on Roman history lately so we’re going to go in on one of the few successful outside threats to the stability of the Roman Empire and the colossally embarrassing reason that saw to the collective sigh of relief by the general populous that had nothing to do with Legionaries but everything to do with a ridiculous amount of bloodshed. So if anyone has a problem with more Roman things, ya’ll can just steppe off, okay? >crickets< Hunny, that was a joke.
If you’re like me, you’ve grown up knowing that the Huns were terrible menaces that could only be defeated by being sung into a man by Donny Osmond. Perhaps because there was a huge wall protecting China named Fa Mulan, the Huns decided the gettin’ was good somewhere else and started off a chain reaction of marauding nomadic assholery by descending upon the Roman Empire in its last legs of life in 4th & 5th century AD. The Romans didn’t know what was happening, or where these demonic barbarians came from–it probably didn’t help that other bands of groups joined in on the fun including the Goths, Alans, Scythians, and anyone else who could rock a ferocious blood-soaked beard. When the Huns and their warband associates began hammering away at Roman territory, the empire found itself stretched thin without a large enough force to defend against attacks along its borders. Rome capitulated some territory and even employed various groups of them as mercenaries to help defend against the Zerg Rush of barbarians. All in all, it seemed a confusing mess of splintered groups with different leaders fighting each other back and forth as long as everyone was well fed and paid while the Roman emperors nervously wringed their hands hoping nobody would depose them since they had been dropping like flies faster than a Hogwarts Defense Against the Dark Arts professor at this point. 
It wasn’t until Attila that the Huns became a unified empire. Most historians assume he murdered the crap out of his brother Bleda before taking the reigns and charging all over the eastern half of the Roman empire in an assault that horse-whipped the once mighty Rome into paying off the Huns with an annual tribute of 2100 pounds of gold to let up a little bit, geez Louise. 
This wasn’t nearly enough for the insatiable Atilla, however, when Honoria, the sister of the Western Roman Emperor, sent him the Classical equivalent to a booty text in the form of a ring and offer of betrothal, and Atilla demanded half of the empire as his dowry proving he was pretty ballsy, if nothing else. He used the opportunity to justify an invasion, sacking and razing the roof all over the place.  (Somebody remind me to do a write up of Honoria some day because she was pretty wild herself)
Unfortunately, things didn’t work out with Honoria, and Attila the Hun eventually took another wife culminating in a raging night of drunken revelry in celebration. And like George R.R. Martin himself wrote it, it was this night that Attila the Hun met his end.
He had given himself up to excessive joy at his wedding, and as he lay on his back, heavy with wine and sleep, a rush of superfluous blood, which would ordinarily have flowed from his nose, streamed in deadly course down his throat and killed him, since it was hindered in the usual passages. Thus did drunkenness put a disgraceful end to a king renowned in war.
– Jordanes, the Gothic History 
A nosebleed?! I suppose, if you’re a subscriber to anime tropes being a thing that actually happens in real-life, perhaps Atilla was a bit too pleased to see his new wife. Most probably, something more akin to a hemorrhage caused by internal bleeding due to excessive drinking was the cause, but I don’t know, I’m not a doctor.
Naturally, the Huns were super upset by this sudden death, and after they ripped out their hair and clawed at their faces, they went to work burying their great king in his riches and killing everyone who helped because why stop being dramatic now. This tactic seemed to work, however, because we still have no idea where he is today. 
It wasn’t long after Attila’s death that the Hunnic Empire collapsed. Turns out, it’s pretty tough to keep a bunch of bloodthirsty warriors in line. And Rome didn’t have that long to neener neener about it either. On September 4th, 476 AD, barely 25 years later, a different barbarian king, Odoacer, deposed the last Roman Emperor and declared himself king of Italy, effectively ending the western half of the empire.
Cause of Death:
Fact Check it, yo!
 Heather, P. (1995). The Huns and the End of the Roman Empire in Western Europe. The English Historical Review, 110(435), 4-41. Retrieved from http://www.jstor.org/stable/573374
 Bury, J. (1919). Justa Grata Honoria. The Journal of Roman Studies, 9, 1-13. Retrieved from www.jstor.org/stable/295986
 Priscus, Fragmenta Historicorum Graecorum. Priscus at the Court of Attila. Retrieved from: http://faculty.georgetown.edu/jod/texts/priscus.html
 Jordanes, The Gothic History Retrieved from: https://archive.org/stream/gothichistoryofj00jorduoft/gothichistoryofj00jorduoft_djvu.txt