> First, some context. Before 1928, countries had the legal right to wage war. If one state claimed to be victimized by another, international law permitted it to use force to right the wrong. International law also gave countries the right of conquest, meaning they could benefit from war by keeping its spoils, territory and, in some cases, people. The right of conquest did not depend on whether the conqueror was in the right. As long as it claimed to have been a victim, no matter how flimsy its argument, the conqueror became the new legal sovereign. It’s easy to see how the right to wage war could be, and was, abused.
First, it's saying prior to 1928, war was OK if the initiator was victimized or it simply wanted to annex a new place. Then it says the victors needed to make up a "flimsy" pretense of victimization in order to keep its winnings. They used to make up flimsy arguments for why they were doing the right thing before 1928, and still do after 1928 (cf. Russia "protecting" its people in Crimea). What part of the "law" actually changed?