The Princess and Curdie
Curdie, the young miner, is sent off to rescue the King and Princess Irene, who are under the sway of evil men bent on taking the kingdom for themselves. The people of the city ignore what is going on and descend towards beastlife. Ends with a new king [after Curdie and Irene] who mines the city for its gold and jewels and ends up bringing about its destruction. A sad ending. One of my favorite books back in elementary school.