The Tsardom of Russia level 3 says: "Ravage Cards also match lands with 3 or more Explorers. (If the land already matched the Ravage Card, it still Ravages just once per Card.)"

If there are two Ravage cards in the Ravage slot, lands with 3+ Explorers match them both. So the land will Ravage twice, as long as it has 3+ Explorers in it.

If there are no Ravage cards in the Ravage slot, then there is no card to match, and no Ravage will occur at all.