In 1950, almost every square inch of Korea's flat river valleys were cultivated with rice paddies. Per the prevailing agricultural techniques at the time, these fields were fertilized with human waste. Fighting a war in Korea involved taking control of the high ground, a task for which trucks and mechanized equipment were useless. The U.S. Army during the Korean War relied on trucks - and therefore roads - for resupply and communications. These roads were rough and, during 1950, clogged with refugees escaping forces invading from the north. Enemy soldiers were exceedingly adept deploying roadblocks and ambushes, taking full advantage of the rough terrain.