[WTRW] You're 9, only interested in non-fiction or action-based semi-historical/myth fiction, and you're out of Rick Riordan books?

So this is for my son. He's 9, and reads on a middle school level. He's read every Rick Riordan book and makes his way regularly through 300 page greek myth or legend anthologies. He's at this point where his interests aren't really age appropriate - he wants to read action-packed accounts of The Crusades, or World War II, or natural disasters and I'd be fine with it if it's not too graphic. He's more mature than his age, but he's still only 9. I'm having difficulty keeping him in books.

He's read every I Survived book, and though I tried to push some non-legend-based fiction he didn't care for Lemony Snicket or the John Grisham Kid Lawyer series. He's read the Amulet Series. Hmm...trying to think of what else we've tried...I'll add things as I think of them.