PTSD has been around probably since the beginning, they just had different names for it.

They used to just institutionalize people that struggled with it, and other things too. Now it is being recognize more, it's not a political thing, it's due to amazing individuals that are actually taking the time to study people that struggle with the same symptoms, and experienced trauma.

It can stay dormant for a long time and then just surface even years after a trauma. They don't know "why" that happens, only that it does happen.