text: At this event, an agreement to set a certain national border at the Curzon Line was made official.
full_question: At this event, an agreement to set a certain national border at the Curzon Line was made official. In the aftermath of this event, one of the involved parties began formulating Operation Unthinkable in case agreements made during this event were not adhered to. This event's agreement to hold fair elections in Poland was completely ignored by one of its participants. All of the delegations at this event agreed to join the United Nations, and one of them agreed to declare war on Japan shortly after this event. For 10 points, name this second "Big 3" conference after Tehran, in which Churchill, Stalin, and Roosevelt met near a resort town in Crimea.
first_sentence: At this event, an agreement to set a certain national border at the Curzon Line was made official.
raw_answer: Yalta Conference [or Argonaut Conference; or Crimea Conference until "Crimea" is read]