Read this: Another important factor is the apparent consensus among Western great powers that military force is no longer an effective tool of resolving disputes among their peers. This "subset" of great powers France, Germany, Japan, the United Kingdom and the United States consider maintaining a "state of peace" as desirable. As evidence, Baron outlines that since the Cuban missile crisis (1962) during the Cold War, these influential Western nations have resolved all disputes among the great powers peacefully at the United Nations and other forums of international discussion.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): What formerly effective tool for international disputes is no longer effective among peer powers?
military force