One famous example comes from the time of the invasion of Philip II of Macedon. With key Greek city-states in submission, he turned his attention to Sparta and sent a message: “If I win this war, you will be slaves forever.” In another version, Philip proclaims: “You are advised to submit without further delay, for if I bring my army into your land, I will destroy your farms, slay your people, and raze your city.” According to both accounts, the Spartan ephors sent back a one word reply: “If.” Subsequently both Philip and Alexander avoided Sparta entirely.

http://en.wikipedia.org/wiki/Laconic_phrase