Every nation has its pride, but the feeling runs especially deep in Iran. There, the sense of nationhood extends back 2,500 years, to the time of Darius and Xerxes and other names that Americans might possibly have heard of somewhere — maybe in the action movie 300 — but which anchor modern Iranians to a stream of history that predates every Abrahamic religion, including Islam, and carries real implications for the nuclear issue. For outsiders, it makes the issue a lot tougher