This thesis is made up of nine chapters. The introduction offers some preliminary discussion of the subject of the period as a whole, and some consideration of existing modern sources upon it. Our modern concept of the ancient world is necessarily constructed from materials derived from reports, and from the various other sources which have survived to use. The purpose of Chapter 1 is to establish how the reports and sources which pertain to the fifth century BC will be evaluated and used in the following thesis. To this end, the work of the three main contemporary historians for fifth century Greece are examined and some concluding comments regarding our use of them for the study of fifth century Macedon are made. Alexander I of Macedon faced circumstances which were almost completely incomparable to those faced by any other king during the period covered by this thesis. The fact that he not only preserved the integrity of his kingdom during the titanic Persian Wars but went on to gain territory, increase trade and improve the Macedonian army to an extent that it could conquer and maintain a vast tract of land, displays a commitment to the wellbeing of his country and a level of patriotism which Chapter 2, alone amongst modern studies, identifies and explores. In his commentary on Thucydides, A. W. Gomme has this to say about Perdiccas’ frequent changes of allegiance: “he chopped and changed all his life, as far as we can see to no very good purpose, except that he kept his kingdom intact and his own throne.” (p201) From Perdiccas’ point of view, and in the context of the Peloponnesian war, during which Macedon itself became, at times, a military objective, keeping his throne and kingdom intact was, in fact, a “very good purpose,” and indeed no small achievement. Chapter 3 explores the dramatic fluctuations in Perdiccas’ foreign policy which allowed him to do this, and considers modern viewpoints upon it.