^^
To be clear, amoral means ‘outside of, or not concerned with moral principles’, while immoral means ‘actively breaking moral principles’.
Machiavelli starts from the premise that the function of a prince is to rule and to guard against threats to his rule. Indeed, if a prince does not do this, he will almost certainly lose his rule and probably his life, too (and probably in a horribly nasty way).
So, Machiavelli’s advice to his prince is to put this function above any moral principle or virtue. In other words, preserving rule justifies breaking any moral principle, no matter how ruthless the course of action may be (betrayals, torture, murder, deception, etc.).
Machiavelli is meticulous not only in his logical arguments but also in supplying hard data from the hard experiences of other princes throughout history who had made fatal errors. With a ruthlessly clear eye, the (in)famous Florentine also shows how a pragmatic prince is better in the long run for his people, too.
‘Ruthlessly pragmatic’ may be used today more figuratively, simply to refer to the compromising of principles and the breaking of alliances when this is necessary to secure a key objective. However, most people would simply call this attitude ‘pragmatic’. It does depend on how idealistic or realistic one is.
