Apakah aku yang dulu? Armin realized that Eren had gained the powers of the Founding Titan and must be leading them to victory over the Marleyans.
King Frits wanted only peace on the island, but he knew that the Marleyans wouldn't allow this.
RELATED: It's possible to argue that they could borrow the knowledge from the un-Rumbled sections of the planet, but even that would take way too much time.
And if that happens, their race will slowly go extinct in a few years.