From the front page....
https://www.cbr.com/star-wars-the-ri...-order-origin/
While we know the basics-that an Imperial fleet led by Hux's father and Grand Admiral Sloane left Jaaku for deep space and built up in secret for decades-from novels and details gleaned from the film itself, it's a bit less clear exactly how things evolved from there, especially with Snoke & Ren taking control. Plus it's never been explained exactly what "First Order" means (Although sometimes the Empire was known as "The New Order").
I'm thinking that Richard E. Grant's character, Allegiant General Pryde, might actually be from the old Empire as well. He seems old enough.