 The invasion caught South Korea and its American ally by surprise, and sent the defending South Korean forces into retreat. The U.S. moved troops from Japan to fight alongside the South Koreans. The first troops landed on July 1, and by July 22, three U.S. Army divisions were in Korea, including the 1st Cavalry Division. These American troops were insufficiently trained, poorly equipped, and often led by inexperienced officers. In particular, they lacked training in how to deal with war-displaced civilians. The combined U.S. and South Korean forces were initially unable to stop the North Korean advance, and continued to retreat throughout July.
