There is in fact nothing that you can realistically expect to do. But you can't just let it go. So following is what you can do:
1. Look for one of your old heroes, who, in addition to all his past heroisms, boasts being a connoisseur of an ancient art of offensive.
2. Design on employing this ancient and esoteric art of offensive to tactically thwart the invading superpower.
3. Build up an army of artists of that art, led by the aforementioned old hero.
4. To make the army most effective, recruit only those who boast origin from the land of the superpower. That way, you will have all the ingredients indigenous to the land of superpower and may expect better to foil their mission.
5. As a step of extra carefulness befriend a general from the superpower and present with an honorary leadership position to the esoteric army.
For an example study the following case:
Dysentry as an offensive