Two groups left Jerusalem 600 BC to escape the Babylonian invasion and utter destruction of their beloved city, totally independent of one another. A much earlier third group left during the confounding of the languages and left from Sidon, Lebanon. See Old World.
The plates containing The Holy Book of Mormon were buried in a hill in Palmyra, New York (420 AD) and retrieved by Joseph Smith (1827). That area was named "Cumorah" by a messenger of God. Joseph said the Nephites were destroyed there. See Cumorah.