Though written at different times, and in response to different occasions, the essays in this book aim to offer a convincing and coherent approach to the interpretation of the topic referred to in the title. The initial impetus for this long course of historical research came in 1976, with a project focused on trade relations between Italy and France in the sixteenth and seventeenth centuries. The results of that project are given in the essay that opens this volume, followed by others that were the fruit of research which, in many ways, grew out of that initial interest.