Trench warfare
Trench warfare prevailed on the Western Front from late 1914 until the Germans launched their Spring Offensive on 21 March 1918. After the buildup of forces in 1915, the Western Front became a stalemated struggle between equals, to be decided by attrition. Frontal assaults, and their associated casualties, became inevitable because the continuous trench lines had no open flanks. Casualties of the defenders matched those of the attackers, as vast reserves were expended in costly counter-attacks or exposed to the attacker's massed artillery. There were periods in which rigid trench warfare broke down, such as during the Battle of the Somme, but the lines never moved very far. The war would be won by the side that was able to commit the last reserves to the Western Front.
7th Cavalry Brigade (United States)
After the brutal trench warfare of World War I, the United States was looking for new ways to engage in armed conflict. As the German Army invaded France, Belgium, Luxembourg, and the Netherlands, the United States military hierarchy realized that an armored division was essential for a modern army. While training outside of Alexandria, Louisiana, the commanders of the 7th Cavalry Brigade met in a high school basement to discuss the creation of an American armored division. Major General Frank M. Andrews, Generals Adna R. Chaffee and Bruce Magruder, and Colonel George S. Patton Jr. agreed to recommend to Washington that the U.S. Army establish its first tank division.