For a week and a Half, Rowan employed his illusion Lantern and his abilities to enslave all 10 million enemy soldiers left and was even able to enslave 7 out of the 14 General (Sages) left. Rasoul told him to try and see if he could enslave the sages too.
The 6 kingdoms brought 22 million soldiers for their first invasion but tragically lost over 12 million. It was a huge loss yet their determination to conquer the Sundance KIngdom hasn't wavered since they are now sending yet another 20 million from the five kingdoms and the Royal guards from the Porter Kingdom.
They are more than determined to conquer at least a single stronghold. That's all they needed to move their armies to the Sundance Kingdom. They knew the Sundance Kingdom lost almost half of their army so their moving over 20 million Soldiers simultaneously was the perfect lineup to conquer the Sundance army.