3. Black Monday

No one is entirely certain about the causes of Black Monday, on October 19th 1987. But what is certain is that billions of dollars were wiped from stock markets across the globe. Hong Kong lost a massive 45.8 percent of its value, the United Kingdom lost 26.4 percent, Australia dropped 41.8 percent, and New Zealand dropped a full 60 percent from its peak.

Some people suggested it was an accident waiting to happen, and theories such as program trading, disputes about monetary policy and fears over inflation have all been proposed to explain what happened. It could even simply have been a panic that spread with no rational explanation. What is certain is that it cost an awful lot of people an awful lot of money.