This is the 13182nd most frequent Turkish word.
katılmıştı
"Katılmıştı" means "had participated" or "had joined" in English.
In this sentence, 'katılmıştı' is utilized to describe a completed action from the past—the person's participation in the conference.
Geçen yıl düzenlenen konferansa o da katılmıştı.
He had also attended the conference held last year.
Here, 'katılmıştı' indicates the past involvement of all individuals in a trip, emphasizing the collective action.
Birlikte yapılan geziye herkes katılmıştı.
Everyone had joined the trip done together.
In this context, 'katılmıştı' reflects the initiation of membership in a team, occurring prior to subsequent events described.