And it came to pass that the Lord spake unto me, saying: Blessed art thou, Nephi, because of thy afaith, for thou hast sought me diligently, with lowliness of heart. And inasmuch as ye shall keep my commandments, ye shall aprosper, and shall be led to a bland of promise; yea, even a land which I have prepared for you; yea, a land which is choice above all other lands. 1 Nephi 2:19-20
Nephi's father, Lehi, prophesied about the destruction of Jerusalem to the people around 600 BC. No one liked what he said, so Nephi moved his family to the Red Sea.
Nephi prayed for direction from God so God blessed him by saying he will give him another Promised Land, a choice land.
God's purpose all throughout the Bible was to save his people from sin. So He showed Abraham the land (Genesis) and said your descendants will prosper here. God led Moses and the Israelites from Egypt (Exodus) to this land and then, with the help of Joshua, David and other military endeavors, drove the enemies out of the land.
All of that happened so a Messiah could come through the line of David and save the world from its sins. He would sit on the throne forever.
The temple in Jerusalem became the focal point of sacrifice, a sacrifice perfected by Christ, making the temple obsolete. But that wouldn't happen for 600 years after Nephi.
So...why would God create a new promised land? Why, after all that work, would God move a line of those people to another part of the world. Certainly war and invasion caused certain tribes to be scattered and wiped out, but God kept true to his initial purpose.
Moving a group of Jews away from the promise seems inconsistent, especially when God was trying everything he could to keep the people together.