This book succeeds the challenge of synthesizing the main conflicts of the last century, conflicts that have forged lasting geopolitics World and we are still feeling the consequences. With talented authors who are authorities on the subject (Pierre Servent, Pierre Razoux ...), causes, ins and outs of twenty wars (some relatively unknown) are analyzed with clarity accessible to all. Some "micro-war" are not addressed (large Chaco, Libya / Egypt, China / Vietnam ..) while it had some local impact but they must make choices. To advise all to understand the world of yesterday, today and tomorrow.