Big crashes don’t happen until the Fed inverts the yield curve.
Disastrous falls in the stock market....all have a history. You can go back to the 1800s and observe each one of these. In most of those...it was a regional situation (a drought, massive flood, a series of regional bank failures). It’s not till 1929 that you have a true national collapse.
But in the 1929 period, you can go through the decade prior and find literally a dozen warning signs. Land speculation, banks taking consumer deposits and speculating on stock, etc. The fed could have stepped in and resolved the 1929 crash and lessen the effect, but failed miserably. FDR came on three years later and simply doubled the effect of the crash.
If you look at 2008, you see almost a whole decade of warning signs...again, land speculation, huge stock expectations, the tech market over-heated, and banks again into heavy speculation.
If you look at Greece and their great fall...there were signs going back two decades. Same for Cyprus.
Right now, I see one colossal problem in the amount of debt owed on college loans. If you have any situation arising where large numbers of people are laid off....the college loan problem will collapse the market and you’d repeat 1929 all over again.