Jerusalem is the capital of Israel, and the most sacred place to the Jews since Biblical times. It is also very holy to the christians due to Jesus' epoch there.
It was first mentioned in "All About Mormons", when Joseph Smith lied to his townsfolk that the Native American angel, Moroni, told him that all Native Americans came to America from Jerusalem.
It was mentioned again in "A History Channel Thanksgiving", when Natalie Portman mentions that she went to "the (Hebrew) University of Jerusalem".
It was first seen in "Ginger Cow", where the 3 Abrahamic religions rejoice at the sacrifice of the Ginger Cow and enjoyed a Van Halen concert to celebrate world peace.