A classic. Along with:

A Polish man finds a genie in a lamp, who gives him three wishes. The Polish man thinks, then says, “I wish the Mongols would pillage their way into Poland, and then go back home to Mongolia.” The genie, confused, complies, and Poland is ravaged by the Mongol hordes.

“Again.” the Polish man says. Dutifully, the genie obeys, sending the Mongols across the steppe to pillage Poland again.

“Again!” the Polish man cries.

The genie complies, but at long last, cannot hold his tongue. “You could have had anything!” the genie says, “Why wish for the Mongols to pillage your own country?”

The Polish man smiles and taps his head. “Ah, but to get to Poland and back to Mongolia, they have to pillage their way through Russia twice.”