This is the 13209th most frequent Russian word.
миротворческого
"Peacekeeping" or "peacekeeping-related."
Here, "миротворческом" modifies the noun "центре," describing its purpose as related to peacekeeping missions.
Он прошел обучение в миротворческом центре ООН.
He trained at the UN peacekeeping center.
"Миротворческая" is an adjective describing the type of mission, emphasizing its goal of maintaining or establishing peace.
Их миротворческая миссия была успешно завершена.
Their peacekeeping mission was successfully accomplished.
"Миротворческую" is the adjectival form directly relating to "операцию," specifying that the operation was aimed at peacekeeping.