The United States has a problem unique to history’s greatest powers. Our wars are often too cheap. Air campaigns like the 2011 campaign in Libya, the ongoing one against the Islamic State in Syria and Iraq, and the drone strikes that periodically target militants in Pakistan, Yemen, and Somalia sacrifice few if any American lives and spend the federal equivalent of loose change.

Because these wars risk so little, or seem to, we have grown too fond of them. We make war without much regard for whether it is worthwhile. Recent U.S. decisions to bomb countries bear less resemblance to the struggle between branches of government that the constitution anticipates than to one-click shopping online, where low upfront cost and ease of delivery encourage whimsical choices uninhibited by debate about value.