During the 1960s, America became embroiled in an increasingly unpopular war fighting communism in Vietnam. Antiwar sentiment led to mass youth protests, which occasionally turned deadly. With the Soviet Union breaking up in the late 1980s, the United States was the sole superpower. But it quickly became the target of Islamist terrorism, as 9/11, the wars in Iraq and Afghanistan, and the War on Terror came to define the first two decades of the new...