After just reading the title:
I’ve been saying this for decades. And now the barbarians (Islam) is at the gate.
Yup.
I think there is a sort of general perception that the Roman Empire fell because it lost some big battles. But that’s not really true. I mean, they did lose some big battles — Adrianople, Chalons, etc. Bu the Roman Empire fell because of massive immigration of peoples into the Empire and their refusal to assimilate.