Nuclear war would most likely end all civilization for thousands of years

 Why?

Well. Because that is what it did on the first timeline to reach 9-11-01 when people freaked out because of what Osama Bin Laden did. This was the real reason Osama was shot (even though he was a double agent CIA agent for the U.S. in Afghanistan helping drive the Russians out of there with Stinger missiles in the 1980s).

So, civilization ended on our first timeline from September 11th 2001 until around 6000 AD because of Radiation poisoning and genetic problems to humans as a result of all this. and where civilization first returned was in the Swiss Alps in this region where because Switzerland and Austria are neutral Countries they were not nuked on 9-11-01.

We here live on the 2nd timeline that I was asked to help build from people from 7028 on the first timeline to prevent the suffering that their timeline caused and the deaths of billions of people within the first month of September 11th 2001 on the first timeline. 

Civilization never recovered for 4000 years after that on the first timeline.