Mosiah 25:24

"And they were called the people of God. And the Lord did pour out his Spirit upon them, and they were blessed, and prospered in the land."

Many groups of people came together and became Nephites.  Each group experienced some sort of affliction in order to get to this point. They all decided to be baptized and show their devotion to God by organizing churches and living righteously.  As they did this they became the people of God and has the Spirit with them!