Key point: A ground war with North Korea would be an extremely complex operation with considerable military and civilian casualties on both sides.
North Korea is just slightly larger than Ohio. To the south it borders South Korea, to the west it borders the Yellow Sea, and to the east it borders the Sea of Japan. To the North it shares an 880 mile border with China and a much smaller one with Russia. The southern border is heavily fortified, with a 2.5 mile demilitarized zone separating the two Koreas. About a tenth of the population resides in the capital, Pyongyang, with the rest primarily residing in cities on both coastlines, often separated by water, hilly or rough terrain.
Any invasion of North Korea would have to take account these geographical realities. The 1.2 million man Korean People’s Army is organized into nineteen corps-sized units, including nine infantry corps, four mechanized corps, one armored corps, one artillery corps, the Pyongyang Defense Command, Missile Guidance Bureau and Light Infantry Instruction Guidance Bureau. More than half of these forces, particularly the mechanized, armor, and artillery forces are located near the DMZ, making an early cross-border assault unattractive.
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The Korean War is unique in that a war has already been fought over the same terrain, against the same enemy, in a largely conventional war. Its legacy suggests that if the United States and South Korea wish to invade the North, an amphibious assault would be the opening blow. North Korea has 1,550 miles of coastline, and while not all of it is favorable to amphibious operations there is plenty that is.