This is the 247th most frequent Turkish word.
katıldı
"Katıldı" means "joined" or "participated" in English.
In this sentence, 'katıldı' is used to indicate participation in an event or gathering.
Ali dün akşam toplantıya katıldı.
Ali participated in the meeting last night.
Here, 'katıldım' implies agreement or concurrence with an idea.
Bu açıklamaya ben de katıldım.
I agreed with this statement too.
In this case, 'katıldı' signifies that countries became part of an organized event.