Behavioural science has an interesting take on why countries like US, Russia are now totally ignoring a rules-based system: old habits change when new rewards seem, even if wrongly, more lucrative than older ones
Charles Duhigg, in The Power of Habit, says that most human behaviour follows a simple loop: a cue triggers an action, a routine follows, and a reward tells the brain if it should remember it. Habits, once formed, do not go away. They can be changed. By swapping in a new routine, while keeping the same cue and reward. This idea also explains why the international order after World War II worked well for a time, and why it is now facing problems. The habit of cooperation has quietly been replaced, by the habit of conflict.