The world reaches Iran nuclear deal.

[Anomalocaris]

Nuclear energy is not against any law.

But building nuclear weapons to destroy a country (Israel) is highly illegal. Iran is doing exactly that.

No, building a nuclear weapon is only illegal because Iran signed onto the nonproliforation agreement, nothing more. Even if destroying a country is illegal, and the nuclear weapon is being built to do just that (which I do not believe to be the case at all), the building of nuclear weapon is still not illegal in itself for any reason except for the fact that Iran has made prior commitments not to do it.