I would like to ask, whether the title "Crashes on Financial Markets" is OK, or should it be "Crashes in Financial Markets"?
A crash and price movements occur in the financial markets.
However, stresses which can cause the financial markets to crash can occur on the financial market.
President Trump's tweet last night has placed pressure on the financial markets. The major markets are trading down today.
I think "Crashes in Financial Market" is the correct phrase. Because, the crashes occur within the financial market rather than something crashing on the financial market.