Agree that the world was safer 40 years ago, but the nuclear powers behavior showed that no state was safe from outside attack unless it had nuclear weapons.
There is no disincentive to acquiring nuclear weapons, rather the contrary. Iran must be desperate to have them, as a deterrent to US and others, just as Taiwan needs to deter China.
Perhaps nations will be forced to compete in other ways. China's gradual influence expansion via loans and salami slicing tactics seem to be the most effective current model.