They will surrender, or at least talk peace if you get their attention. Cut off lux or resources.. Have another civ attacking from the other side. First city I took from Russia, eg, took their one source of saltpeter. They immediately sued for peace. Egypt i took 6 cities on the first turn, but they would not talk to me. Once I had pushed them off my continent, I had no further interest, and eventually they listened, and signed peace. First time. SEcond time, I just got tired of them poking around ("We wer just testing your defences. We will leave directly." WHen I cut them down to 4 cities, and was thoroughly tire of the war, I went to her. Then she said, "Lets end this bloodthirsty war..." I demanded and got one city. England declared war on me... and held out to the bitter end. Actually she had four cities, but in the face of overpowering forces, she was facing anhiliation... and knew it. She sued for peace, and gave me three of her four cities.
I know I may have trouble from them later, but I really don't like genocide. And in a position of power, I can afford to be generous.
To answer your question: How to make them talk to you... Either hurt them bad and fast, or back off and leave them be. eventually they will sue for peace.