Here are some examples:

Example #1

You have several Infantry Spirit Wardens, with each one having a defense of 200. A player attacks your Castle with 2 Pikemen. Each one has an offense of 40, bringing the total offense to 80.

The offensive power of the 2 Pikemen (80) is less than the defensive power of one Spirit Warden (200), so the Spirit Warden will defeat the Pikemen and live to fight another day.

Example #2

You have one Infantry Spirit Warden with 200 defense and one Divine Spirit Warden with 350 defense. A player attacks your Castle with one Knight and 7 Pikemen. The Knight has an offense of 240 while each Pikeman has an offense of 40, bringing the total Infantry offensive power to 280.

In this case, the battle will be divided into two parts.

The Infantry Spirit Warden will engage first, followed by the Divine Spirit Warden.

The offensive power of the 7 Pikemen (280) is more than the defensive power of one Infantry Spirit Warden (200), so the Spirit Warden will be destroyed.

After this, the Pikemen and the Knight will engage the Divine Spirit Warden. Since the first Spirit Warden fell, the new mechanics won't apply here. So, the Divine Spirit Warden will be destroyed after engaging the attacking Units.

Example #3

You have several Infantry Spirit Wardens with each having 200 defense, and several Divine Spirit Wardens with each having 350 defense. A player attacks your Castle with one Knight and 4 Pikemen. The Knight has an offense of 240 while each Pikeman has an offense of 40, bringing the total Infantry offensive power to 160.

(^.^)