Since the Trump team labeled its foreign policy “principled realism” before carrying out much of it, the term is not a description of things accomplished. Instead, it tells us how the Trump team wants to regard the policies it may pursue and, above all, what it wants others to think of them. Being a label applied to an as-yet largely empty container, it is advertising.

Consisting of three books, of sixty, thirty-three, and forty-nine chapters respectively, the Discourses contains the bulk of Machiavelli’s teachings. Unlike The Prince, the chapters are written plainly, headlined in Italian rather than in Latin, and addressed to persons he deems sympathetic to those teachings. The subject is nothing less than what makes for successful states and individuals, as well as for success in war. It is covered on high, low, and intermediate levels of specificity. The format is a series of observations apparently chosen almost at random.

The Prince, Machiavelli’s best known and least understood work, consists largely of anecdotes of victory and defeat in conflict. It is neither a set of recipes for success, nor an argument in favor of harsh methods. That is because Machiavelli’s anecdotes suggest that different—indeed opposite—approaches to conflict are likely to bring victory or defeat according to how well they fit the particular circumstances in which they are used.

In the middle of May 2003, the U.S. government threw away a victory that its armed forces had won and started a new war that it had no idea how to win. This fortnight’s events remind us that the lack of unity of conception and command can turn victory into disaster.