Two centuries ago, you had nearly 5,000 troops per square kilometer of battlefield. The declined to 3,900 150 years ago, to 404 in World War I, 36 in World War II, 2.34 during the 1991 Gulf war, and today, it's down to less than two per square kilometer. Without sufficient space, modern combat units cannot realistically practice for war. Without that practice, more troops get killed the first time they do it for real, while being shot at.
This progression in spreading troops out is another reason I was not too upset that we went to a brigade combat team of two line battalions.
UPDATE: Many years later I found this chart that illustrates the trend:
Tip to TDI.
