In his State of the Union address to the Congress in 2002, President George W. Bush famously described Iraq, Iran and North Korea as an "axis of evil." In the years since, however, America has not treated each in the same way. The differences are highly instructive.

Bush and his hard-line advisers believed that only force or "regime change" would stop these "rogue" states' terrorism or their programs to acquire "weapons of mass destruction." So, in March 2003, the United States invaded Iraq, resulting in a state of near-constant civil war for over a decade; an ineffectual central government in Baghdad; and now the rise of the Islamic State extremist group.

In Iran, then-President Mohammad Khatami, a political moderate, offered what might have been a reasonable deal to curb the country's nuclear program. But Bush and his team preferred to pressure Iran with sanctions and military threats, and any hope for a negotiated solution vanished when Mahmoud Ahmadinejad succeeded Khatami in 2005. It was only when another moderate president, Hassan Rouhani, took office in 2013 that hope for a negotiated solution could be revived.