I've always been taught it's « arriver à quelque chose » so I'm a little confused why in this video at 23 seconds the presenter says the line « comment en sommes-nous arrivés là » not « comment y sommes-nous arrivés là » or just simply « comment sommes-nous arrivés là » without en or y because I would've thought the là was enough to indicate some sort of position. Could someone explain why it's « en » and what the difference between the three options are (or if my suggested ones are just invalid)?
"En" wears many hats but here it seems to be an adverbial pronoun that denotes initial situation or place:
Comment en (= from where we were) sommes-nous arrivés là (= to this current state)?
The sentence: « Comment y sommes-nous arrivés là ? » is incorrect because “y” and “là” are redundant.
« Comment sommes-nous arrivés là ? » is correct but you lose the expression of contrast of the first sentence.