after
as a conclusion of
Structure
- Verb[た] + すえ +（に）+ Phrase
- Noun + の + すえ +（に）+ Phrase
[A末にB is used when, after a long-lasting/constant situation or activity, something has been achieved or some kind of decision has been made]
I attempted to answer this grammar point with てから (to mark that something happened before another) and was marked wrong. Is this an ambiguity in the question? Wondering if there’s a way to know which one is being asked for and why.