In the first chapter of *Harry Potter and the Sorcerer's Stone*, Albus Dumbledore says:

> 
> "You can't blame them," said Dumbledore gently. "We've had precious little to celebrate for eleven years."
> 
> 
> 

I've read these books at least seven times and somehow missed this. Voldemort was around a lot longer than 11 years prior to Harry being a little baby (infant? toddler?). So why were the previous 11 years so special/bad? Hadn't he been doing awful things for 50+ years prior?

Harry was born in July of 1980 and Sybil Trelawney's prophecy happened in 1979, so not 11 years prior to when Albus, Minerva, and Hagrid dropped off Harry at the Dursley's house in ~October 1981.

So why were the 70s so bad for the magical world?