Why in below sentence writer has used past perfect tense i.e. since Daesh had taken?
This was my third trip to Iraq in 10 years and my second since Daesh had taken over several areas of the country.
As per my knowledge we can use present perfect:
This was my third trip to Iraq in 10 years and my second since Daesh has taken over several areas of the country.
Because Iraq is presently in the possession of Daesh.
Or simple past tense here:
This was my third trip to Iraq in 10 years and my second since Daesh taken over several areas of the country.
Because I think there is no need to explain which event happen first and which second.