To be Historically accurate this key bit of information would help or links to short summaries/blogs that detail the reason for the falls might help and what is the most accurate history of these events?

Fall of Rome podcast

History of Rome by Mike Duncan (another podcast)

Those are good places to start

Found this Vox article that highlights the impacts of volcanic driven climate change and plagues https://www.vox.com/the-big-idea/2017/10/30/16568716/six-ways-climate-change-disease-toppled-roman-empire