On the Shia/Sunni divide

The Tablet

The link is to a pretty good article in The Tablet talking about the Shia in the Middle East, and what the future may hold. As a summary of who is where, and who holds political power, this paragraph is useful:

Shia beliefs are held by perhaps one in 10 Muslims today - some 140 million people. Only Iran is overwhelmingly Shia, where they form 90 per cent of the population. Across the Persian Gulf, the littoral states with significant proportions of Shia include Kuwait, with 30 per cent of its population, Bahrain with 75 per cent, Saudi Arabia with 10 per cent, Qatar with 16 per cent and the United Arab Emirates with just 6 per cent. Approximately half of all Shia live in the arc beginning in Lebanon, with 45 per cent of its population being Shia, and ranging through Iraq with 60 per cent, Azerbaijan with 75 per cent, Afghanistan with 20 per cent to Pakistan, also with some 20 per cent.

In Syria, the ruling elite is Alawite, a Shia- affiliated group with just 15 per cent of the country's people. Alawite domination has bred deep resentment among many of Syria's Sunni Muslims who constitute 70 per cent of the population. Uprisings by Sunni Islamists in the early 1980s were partly fuelled by this sectarian divide.

The author suggests that (as I had said somewhere in comments before), the invasion of Iraq should logically be only a positive to Iran, due to the empowerment that it gave to Iraqi Shia:

Despite the history of Iraqi nationalism, Arab and Persian mutual suspicion and the legacy of the Iran-Iraq war, Iran is not displeased with the changes in the region and will not want to "rock the boat" irredeemably. Before recent changes, Iran considered itself surrounded by hostile Sunni states: Iraq and Saudi Arabia to the West and Afghanistan and Pakistan to the East. It would not want to see "anti-Iranian Arab nationalism" championed by Sunnis to emerge as a threat.

But if that is the case, why is it acting so belligerently about the having an un-monitored nuclear enrichment program?