Answer:
People had money to spend on entertainment.
Explanation:
If that isn't right then do this answer:
The government used military technology to encourage it.
<span>Burning fuel in factories releases acid pollutants. When they mix with moisture, the pollutants fall to Earth in the form of acid rain.</span>
You need a variable. If something happens once it could just be chance. Like if you got a lottery ticket and won, it would just be chance. Not the thing that happens the most.