I have just finished this book, it has been a very interesting and enlightening read, especially for someone who knows very little about international law. As an academic I was also impressed by the careful, measured tone of the arguments made and the importance the authors evidently place on backing up their views with data, as far as possible. This passage sums up the argument, more or less…
The End of Interstate War
For hundreds of years, war shaped and reshaped the world’s borders, moving the lines back and forth, causing states to grow and shrink. It created and destroyed empires. It generated new countries out of the ashes. It ravaged populations, razed property, decimated lives, destroyed livelihoods. And it was accepted not just as unavoidable but as the appropriate legal means of resolving disputes.
After 1928, that changed. For the first time in history, states refused to recognize conquests. Once the Second World War had ended, all but one of the unrecognized conquests were reversed. And after 1948, conquests and international wars dwindled to a small fraction of what they had once been.
In short, the Peace Pact formed the background of rules and assumptions against which the rest of the new system operated. As states adapted to the transformed legal order, their adaptations helped reinforce those new rules and became reason of their own for playing by them. The Pact did not bring about the end of conquest and interstate war on its own; no treaty, no law could have. But it was a necessary start, the beginning of the end of the Old World Order. (Hathaway & Shapiro, 2017, p. 335)
For someone who had no idea about international law this has been a great introduction to the ideas and principles behind thinking on conflict and war, how it has changed and why we operate in the international environment we do today. For beginner students of International Relations, this is essential reading (I would say).