Over the past few decades, the U.S. military has had to shift its focus several times as the security environment and American national interests evolved. Until the end of the Cold War, it concentrated on preparing to fight the Soviet Union, potentially with nuclear weapons. In the 1990s, most of the military’s attention was on conventional wars against what were called “rogue states,” particularly Iran, Iraq and North Korea. After the 9/11 attacks, the U.S. military retooled for counterinsurgency and counterterrorism. Now that era, too, is ending.
Today, as the United States disengages from Iraq and Afghanistan, and Russia and China expand their military capabilities, the American military is again preparing for conventional war. The driving idea in Washington is that U.S. military dominance deters potential adversaries. “The surest way to prevent war,” according to the 2018 National Defense Strategy, “is to be prepared to win one.”
Yet while the Pentagon is shifting to conventional warfare, political leaders have lagged behind and not yet developed clear policies to turn American military prowess into effective deterrence. This needs to be addressed. The first step is to develop a basic understanding of how the United States might become involved in a big war, particularly the indicators and warning signs. The only way to do that is by mining history. The past never provides a precise roadmap to the future, but it can offer hints and signposts. Evidence from the 20th century suggests that three things can lead to a major war.