How we change what others think, feel, believe and do
Machiavellianism is the use of the general principle of 'the ends justifying the means'. This means the Machiavellian person considers their goals to be of prime importance and that any method may be used to achieve them.
The more extreme the Machiavellianism, the greater the harm the person will be ready to indirectly (or perhaps directly) inflict on others to achieve their own goals.
The Machiavellian approach includes using deception, manipulation, theft and, in the extreme, even physical coercion or murder.
Niccolò Machiavelli (more fully, Niccolò di Bernardo dei Machiavelli) wrote 'The Prince' (Il Principe) in 1513, during the turbulent days of the Renaissance Medicis, as a set of pragmatic instructions to a new prince on how to gain and retain power. The originality of his ideas has been challenged and shown to go back at least to the Athenians, yet the influence of Machiavelli's words still rings around the world.
Machiavelli separates public and private morality. People in public office often need to appear to have high morals, yet to succeed they may have to use questionable methods. While many have viewed it as immoral (and hence evil), Machiavelli's views are more amoral. The approach is pragmatic, doing what is necessary to achieve goals, and is an honest description of what many people do.
What is described now as Machiavellianism is more about individual action rather than that of a person in political office, although politicians are often still described as being Machiavellian.
Machiavellianism is not a defined personality disorder, although the extreme forms of it may be classified as Antisocial Personality Disorder.
Machiavellianism is a part of of what is called the 'Dark Triad' which also includes Psychopathy and Narcissism. The common thread that runs through these is a selfish view that cares little for other people and will allow or enact harm to others in the pursuit of personal goals.
Machiavelli, N. (1988). The Prince, Q. Skinner and R. Price (eds.), Cambridge: Cambridge University Press.