Which lyrics are most important in billy joel's song we didnt start the fire?

Hey there!
This song was one of Billy Joel's hits. It covered history from as far as a hundred years ago in a very rhythmical format and catchy tune.
In my opinion, the most important lyrics are:

Hypodermics on the shores, China's under martial law
Rock and Roller cola wars, I can't take it anymore.

This shows to me, after all the terrifying things through history Joel has gone through, the fact that he "can't take it anymore" makes perfect sense and really shows the point of the song.
There's more of these specified terrifying events throughout the entire song, be sure to check them out for yourself.
Hope this helps!