If you're not a Muslim, ask yourself this: which is better, Shia or Sunni?
The distinction between the two arose from a dispute as to who should succeed the prophet Muhammed after his Death in 632.
In Syria and Iraq, before Western intervention, there existed the strange state of affairs that Syria was a predominantly Sunni country with Shiite rulers (the Assad family) whilst Iraq was a predominantly Shia country with Sunni rulers (Saddam family). I have written before that a great deal of unpleasantness could have been avoided if they had simply swapped leaders.
But no, the West intervened and Iraq elected Mr Al Maliki who was going to be an inclusive figure for all Iraqis but turned out, as son as the troops left, to be simply pro Shia.
So the Sunnis rebelled and some of them crossed over from Syria where they had been fighting Assad.
And now some of our half-witted politicians, and the pseudo-statesman Tony Blair, are bleating that we should intervene. And this is where the question at the start of this post becomes important: on which side? Should we intervene in favour of the Shias, allied with Bashar al-Assad, Russia and Iran, or on the Sunni side alongside the ISIS militants, who were chucked out of Al Qaeda for being too brutal?
The answer is that this being a purely sectarian war we shouldn't intervene at all, but let them get on with it. Tony Blair says that we will suffer terrorism in the future, but we suffered a lot when we intervened in Iraq, because those Islamists who are looking to resurrect the Caliphate felt we had invaded their country. We are not going to get more terrorism by not taking sides.
They will not create a united Muslim caliphate in the middle east because they can't stand each other. Long may it continue.