I think you know where I’m going with this one. It’s not uncommon in YA stories – it’s one of the ways that they get the younger generation to drive the story.
It can be quite literally taking command over an army – like Jiaan in the Farsala Trilogy by Hilari Bell when the Hrum army decimated the original Farsalan army.
Or maybe it’s driving out old leadership as in the case of Kaz from Six of Crows by Leigh Bardugo when he took over the Dregs from Per Haskell because he was getting too fat and lazy in the position.
Sometimes they could be aided by a prophecy or their own bloodline that gives them the ability to take over. Cinder of the Lunar Chronicles by Marissa Meyer was a long lost princess, allowing her to take over Luna.
However they get there, the young people now have to make the life or death decisions, not only for themselves, but for they’re followers. It’s a lot of responsibility. But that’s why it appeals to a Young Adult generation who is just learning about the responsibilities of Adulting. This gives the reader a bit of insight and knowledge to help them face these new decisions that have to make every day.