How does a wizard fight an army?

[JackPhoenix]

But not within the power level the PHB recommends for the DM to use: "the effect of any cleric spell or cleric domain spell would be appropriate." (PHB p59)

That's great... so show me what cleric spell would help the cleric to deal with an army. None? Well, I guess the god will have to find a different way to help his favorite servant.... "would be appropriate" isn't the same as "is the only possibility"

Edit: Actually, you know what? One cleric spell is sufficient to deal with an army. The deity uses Gate to drop a horde of celestial superbeings (invisible or not) to deal with the enemy. Suck it, BMX Bandit!