American teenagers have never known their history.
Has it ever occured to anyone that one of the reasons young people struggle with history is that it is hard? It takes a lot of repetitive work to keep track of even the most basic narrative lines of American history, not to mention World History or Western Civ or anything else.
For me, gaining a comfort level in history came in fits and starts. I would pick up on something I found interesting--like D-Day or Pearl Harbor or the Emancipation Proclamation--and then I would build out from those events. Eventually these dots of knowledge began to connect, but it took a long time, and I'm still working at it and always will be.