Let's see if I can break this down:
So, this:"Former prime minister Tony Blair has conceded there are "elements of truth" to the accusation the Iraq War led to the rise of Islamic State, as he once again defended the 2003 invasion.""He also apologised "for some of the mistakes" made in respect to the war, which led to the toppling of Saddam Hussein." 
is linked to this being widely reported a few days back:"Tony Blair said he would support the US if military action was needed in Iraq, the then-US Secretary of State claimed in a memo written a year before the war began." 
Apparently, Blair didn't need any evidence or proof of WMDs to support war in Iraq, all he needed was Bush saying that a war should happen. So it would appear that desire came before evidence, the cart before the horse.
cart was made of high explosives and led to the death of tens of thousands, if not hundreds of thousands, the collapse of a country, which has never really recovered, and led in a direct line from the invasion to ISIS, who’s ranks have been greatly swelled with ex Iraqi military, who had become insurgents fighting the Americans and British after being dismissed by the invaders.
Despite the protestations of Jeb Bush recently, there is no doubt that the invasion of Iraq and the subsequent clusterfuck were directly responsible for the eventual rise of ISIS. 
Blair may well try to justify his position, as he has done countless times, by arguing that it's a good thing that Saddam Hussein was taken out of power and executed. However I'm not sure the roughly 150,000 Iraqi civilians who have died would agree, were they able to talk from beyond the grave 
Certainly, the void created in the middle east allowed for the rise of ISIS, and a further roughly 30,000 civilian deaths in Iraq alone, in the last three years. 
ISIS have gone on to kill tens of thousands more. Of course, maybe Blair is not so bothered about that, since the majority of people ISIS have killed, in increasingly barbaric fashion, across the region are Muslims, 
and Blair doesn't have to account to them (despite, somewhat ironically, being the Middle East peace envoy for eight years - a post in which he achieved precisely nothing at all 
Maybe that was because he was too busy making millions giving advice to other murdering dictators 
Oh, Saddam, if only you had been white and European, Blair might not have agreed to have you killed.
Of course, Blair agreeing to back Bush in a war before there was any evidence for going to war in Iraq is hardly news, given it was reported in 2002 by The Guardian, 
but then the media - as was demonstrated in the years after - were not really listening, and these reports were drowned out by war drums and cheerleaders, so it mostly slipped past.
That said, it probably wouldn't have made any difference to Blair if it had been made a big deal of, given that less than a year later, between 750,000 and two million people marched on the streets of London against going to war in Iraq, and he didn't even bat an eyelid. 
In fact, it wasn't just Blair ignoring the raised voices - the largest coordinated marches in history took place in 2003, across dozens of countries, against war, and it made no difference at all. 
All of this brings us full circle, as, after a ridiculously long time has elapsed, we may finally see the publication in the UK of the Chilcot Enquiry, in which Blair is expected to be excoriated for his part in the disaster (along with many others) we now know the Iraq War was, both at the time, and ongoing for the region and the world. 
And thus we now have Blair halfheartedly apologising for his role in this disastrous affair, spinning for all he is worth. 
Of course, the problem with these half apologies is that they are completely unbelievable. Nobody seriously
believes that if there was no Chilcot enquiry Blair would be giving even this much of an apology. He, like Rumsfeld and Cheney in the US, simply does not see that he did anything wrong, and is convinced, in his head, of his own righteousness. He wears it like armour. That, and the millions of pounds he's made advising dictators he didn't
help have killed, keeps him happy.REFERENCES http://www.itv.com/news/2015-10-25/tony-blair-apologises-for-iraq-war-mistakes/http://www.independent.co.uk/news/uk/home-news/tony-blair-supported-military-action-in-iraq-a-year-before-the-war-leaked-emails-suggest-a6698596.html http://historynewsnetwork.org/article/159589 https://www.iraqbodycount.org/ http://edition.cnn.com/2015/01/01/world/meast/iraq-civilian-deaths/ http://www.thedailybeast.com/articles/2014/10/07/isis-s-gruesome-muslim-death-toll.html http://www.middleeasteye.net/news/analysis-blair-s-eight-years-middle-east-peace-envoy-wasted-1321981501 http://www.telegraph.co.uk/news/politics/tony-blair/11052965/Tony-Blair-gives-Kazakhstans-autocratic-president-tips-on-how-to-defend-a-massacre.html http://www.theguardian.com/world/2002/jul/27/usa.politics http://www.telegraph.co.uk/news/uknews/1422228/One-million-march-against-war.html http://world.time.com/2013/02/15/viewpoint-why-was-the-biggest-protest-in-world-history-ignored/ http://news.sky.com/story/1541698/chilcot-report-blame-to-extend-beyond-blair http://www.theguardian.com/uk-news/2015/oct/25/tony-blair-sorry-iraq-war-mistakes-admits-conflict-role-in-rise-of-isis