Leadership has been defined as "organising a group of people to achieve a common goal", and much of the early writing on the discipline had a military angle. Xenophon, for example, laid down an early marker in his book Cyropaedia, in which he describes in detail the organisation and leadership required to run a great army.
For hundreds of years, most thinkers followed the "trait" theory of leadership, which propounded that great leaders were born and not made, and that leadership was rooted in the characteristics that certain individuals possess. But in the 1940s and 1950s, this theory was challenged – it was argued that while some traits were common across a number of studies, the overall evidence suggested that people who were leaders in one situation might not necessarily be leaders in others.