Ruin
Fall, Collapse
noun, verbal noun
A building or civilization that dies and then falls is in a state of ruin and collapse. Like the Mayans or the Western Roman Empire. They fell pretty hard.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
本当に日本は没落していると思いますか？
Do you think Japan is really collapsing?