Two Consecutive Quarters of Negative Growth
Question: "What causes night?"
Answer: "When it gets dark."
In that case, there is literally only one way that happens: The Sun setting
There are literally so many different factors that can cause a recession on the other hand so the technical answer is the only proper answer you can give to such an open ended question.
Is it possible that recessions happen because they're structural corrections which are bitter pills? What do you think should be done to mitigate or prevent them, is it a good idea to even try?