North Korea sent a fax to South Korea's defense ministry on Thursday, threatening "a merciless retaliation without warning" in response to an anti-North Korean demonstration that had taken place in Seoul.

The story is humorous and revealing for several reasons. First, the idea of scolding the South Korean government for a popular demonstration that occurred within South Korea betrays either a total misunderstanding of how democratic societies function or simply that Pyongyang thought that would be a sufficient excuse for its latest threat.
Second, faxes are funny. The mode of communication is both outdated and entirely undignified, which is actually sort of a perfect metaphor for North Korea's obsolete military and its systematically bizarre practices. (Although the fax is unusually common in East Asia, particularly Japan.)
But my favorite aspect of this story by far isn't North Korea's fax threatening to launch a war at any moment. It's the fact that South Korea, on Friday, turned around and sent the North Koreans a threatening fax right back.
"We've sent a reply vowing to react sternly to any provocations by North Korea," a South Korean defense ministry spokesperson announced. We have not learned the full content of the fax, but it did promise "resolute punishment" for any North Korean provocations.
North Korea does crazy-looking stuff all the time. Behaving in as aggressive and unpredictable a manner as possible is official North Korean strategy. It's by all appearances deliberate, and it's very effective, successfully deterring the North's much more powerful enemies and extracting regular concessions from them. In short, North Korea's crazed war fax is, in a sense, actually pretty rational.
You can't really say the same for the war fax that South Korea sent in return. South Korea's population is twice the size of the North's, and its GDP is 80 times larger. Eighty! It's also got tens of thousands of U.S. troops stationed in the country and a pledge of U.S. support in the event of war. South Korea doesn't need to send an angry fax threatening North Korea. But it did.
North Korea's policy of aggression and random threats serves a strategic purpose. South Korea's own history of hard-line policies has been strategic, as well, but also often earnestly felt.