Ever since the beginning of this (19th) century, the condition of industry has constantly fluctuated between periods of prosperity and periods of crisis; nearly every five to seven years, a fresh crisis has intervened, always with the greatest hardship for workers, and always accompanied by general revolutionary stirrings and the direct peril to the whole existing order of things.

Engels, The Principles of Communism, 1847

Now now, don't also forget once-in-a-generation natural disasters

Communism doesn't work, by the way.