Equestria is fighting her first World War after the 2nd Industrial revolution. She hasn't fought a war in a while. Before his death, Discord enlists the help of several creatures that are all too familiar with the concept.
Honor, Faith, Land, and now... Ponies. Wars are fought for a lot of reasons—and on most battlefields, you’ve gotta find your own. Luckily, my friends and I trampled on a really good cause when we got here...
The dragons were thought to have died out. All the dragon riders were dead. It is said that dragons aren't real, Only two people remain that knew about the dragons