One of the Middle East’s oldest conflicts has entered a new era

Now the region waits nervously again, this time to see when and how Israel conducts its almost inevitable response. Its partners in the West, particularly America, must strike a delicate balance between defending their ally and restraining it. Friendly Arab states are in an awkward position, too. And the belligerents themselves, Iran and Israel, must now navigate a conflict in which the old rules of engagement have been abruptly shredded.