As the United States rebuilt in the aftermath of the Civil War, total Army strength grew relatively slowly until the mid 1900s. The World War I era saw the creation of several important Army branches, including the Veterinarian Corps, the Chemical Corps, and the Aviation Section within the Army Signal Corps, the precursor to the Air Force. World War II led to several more milestones in Army history, including the creation of the Office of Strategic Services, which became the CIA, and Franklin D. Roosevelt's introduction of the G.I. Bill. Two years after the war, the Army established the Medical Service Corps, later renamed the Army Medical Department (AMEDD). Following World War II, America entered a standoff with Soviet Russia, known as the Cold War. During the 1980’s, the Army began to reorganize to focus on training and technology. In the next ten years, the Pentagon introduced plans to reduce total Army strength. In 1989, the fall of the Berlin Wall signaled the end of the Cold War. In 1991, American and allied forces responded to Saddam Hussein’s invasion of Kuwait. The ground campaign lasted four days before a ceasefire was declared. After the attacks of September 11, 2001, American and Iranian forces would again enter into a conflict in the Middle East against terrorist forces in Iraq and Afghanistan.