Usually crashes are the result of manipulation and market being tired of going up. People are starting to have second thoughts and are prone to selling. If at the same time somebody spreads fake news like the one about Korea banning Bitcoin you got yourself a huge selloff.
I strongly agree on your opinion that, usually crashes are the result of manipulation and market being tired of going up. And people are starting to have second thoughts and are prone to selling. And adding also my opinion that, the bitcoin price sometimes goes down quickly because too many people want to sell at the same time, they do that when they are driven by fear. In addition, recently bitcoins prices increased a lot in very small period of time within 1 year bitcoins prices went from $900 to almost $20k so this drop in price was merely because of correction of the bitcoins price. On the otherhand, Bitcoin is still a new product which is still unregulated in some parts of the world and if it is to be used by people without fear we need regulations but the problem is if the people in charge of putting these financial rules.