Blair railroaded the UK into an illegal war. He abused the position of Prime Minister to solemnly go on TV and tell us that the UK faced an existential threat and that anybody who disagreed was a danger to the UK.
I watched that and I thought "Much as I dislike the guy, no one would ever lie at that scale. You can be too cynical".
Turned out I was wrong.
And because it's all an old boys club, successive premiers have failed to call that out and just bumbled along as it it was nothing to see.
That's my opinion. That's my worldview. Others are available.
No one can be sure. But the regional instability that resulted from USUK involvement in Iraq and Afghanistan - all in pursuit of a Saudi Arabian bad boy is certainly one of the drivers for refugees. And if you are a 20-something Afghan man living in Afghanistan thinking "OK, it wasn't heaven on earth but pre 2003 things weren't anywhere near as bad as now" then you too might want to head for the land of the people who fucked your country over. If for no other reason than you probably learned their language when they were patrolling your streets.
You know how many times the old "Why don't they stay in France ?" line is trotted out ? One of the reasons is that French soldiers were not patrolling Kabul.