H. Liepmann 
Tariff Levels and the Economic Unity of Europe [PDF ebook] 
An Examination of Tariff Policy, Export Movements and the Economic Integration of Europe, 1913-1931

The years between the Wars saw rapid and far-reaching changes to the character and distribution of the world’s trade. Governments of the world attempted to mould and control their own economies, and economic nationalism grew to unseen levels. This book, first published in 1938, is the comprehensive examination of the European tariffs of the time, and it traces their effects upon the actual course of trade, and in so doing, is one of the few factual studies on the reality of tariffs.