Things I Did Not Know

On the subject of the artillery shelling in Korea:  The origins of the North-South Korea division -- pretty much an arbitrary line drawn on a map by staffers at the end of WWII:

The Chief of the Policy Section, Col. Charles H. Bonesteel, had thirty minutes in which to dictate Paragraph 1 to a secretary, for the Joint Staff Planners and the State-War-Navy Coordinating Committee were impatiently awaiting the result of his work. Colonel Bonesteel thus somewhat hastily decided who would accept the Japanese surrender. His thoughts, with very slight revision, were incorporated into the final directive. [17]
Bonesteel’s prime consideration was to establish a surrender line as far north as he thought the Soviets would accept. He knew that Russian troops could reach the southern tip of Korea before American troops could arrive. He knew also that the Russians were on the verge of moving into Korea, or were already there. The nearest American troops to Korea were on Okinawa, 600 miles away. His problem therefore was to compose a surrender arrangement which, while acceptable to the Russians, would at the same time prevent them from seizing all of Korea. If they refused to confine their advance to North Korea, the United States would be unable to stop them.

At first Bonesteel had thought of surrender zones conforming to the provincial boundary lines. But the only map he had in his office was hardly adequate for this sort of distinction. The 38th Parallel, he noted, cut Korea approximately through the middle. If this line was agreeable to President Truman and to Generalissimo Stalin, it would place Seoul and a nearby prisoner of war camp in American hands.

Strangely enough, I learned this from Wonkette, the vulgar political satire site.