Morgenthauís book came after his plan, upon which the Allies based their treatment of Germany after World War II. Although in the course of time that plan was modified, it was really abandoned only when Germany started to be involved in what was going to become the European Union. This move meant for the USA that Germany ceased to be a threat to the peace of the world.
Reading the book Germany is our Problem, one is surprised by the sharp thinking of its author, a minister of the Roosevelt administration. It is a book indicating the high level of political thinking in the USA of that time, and is also a book that helps us understand the forces which permitted the German horror of World War II, forces springing mainly from inside the German character.
For us today, when Germany is, at least for the moment, a part of the European Union, this book is useful not so much in order to protect ourselves from a possible German military attack, an attack rather destined to be crached under the present balances of power, but mainly in order to understand a partner of ours, to know better the German character, ambitions, ideals, all of which necessarily participate, even if transformed, in Germany's current policies and decisions.
Reading this book we must not forget that inhuman and inferior forces exist in all nations as in all men. However, beyond a non-existing point of a complete innocence, there are differences and degrees in a nation's sharing of such forces. The purpose of knowing these differences is to make us more determined in helping each other and all of us to defeat our inferior self.
If you have to read just one chapter, let me suggest Germany Has The Will To Try It Again, because in this chapter the author explains the horrible form of German aggression by examining some of Germany's influencial thinkers.