What made the Mormon religion change their mind about allowing black people to hold the priesthood?

Answer 1

The Church of Jesus Christ of Latter Day Saints (commonly called the "Mormon" Church) did not allow blacks of African decendency to hold the priesthood until they received revelation from God that they could. Church members of all races had been praying for this revelation for decades, and most were very upset at the situation. Finally, in June 1978, the First Presidency and Quorum of the Twelve Apostles announced that they had received revelation from God while meeting in the upper room of the Salt Lake Temple that blacks of African decendency could now be admitted into the priesthood.

Please note that blacks could always be members of the Church, they were just not permitted to hold priesthood positions in the Church. Also, dark-skinned people of other ancestry were admitted into the priesthood prior to the revelation.

Answer 2

Interestingly, for a practice that has caused so much controversy, there was never any doctrinal basis. The practice arose out of an unfortunate confluence of geography, persecution, and habit. When the Latter-day Saints were driven from place to place, they ended up for a time in Missouri, a state where the question of slavery was hotly contested. The practice of not ordaining Blacks to the priesthood appears to have originated in that atmosphere. When the Saints were driven out of Missouri under threat of extermination, and then again out of Illinois with the same threat, they ended up in Utah. There were only a couple of Black Mormons in that trek, and the sole male black Mormon was actually ordained to the priesthood. The question didn't arise again for several decades, inasmuch as the Saints were simply trying to eke out a living in the high mountain desert. When it did arise, the simplistic "We've always done it that way" turned into official practice. Blacks were baptized, but men weren't ordained.

In 1978, when the Church grew larger and the question became more pressing, the president of the church went to God in prayer and fasting, and asked for specific instruction on the matter. He received revelation that the practice of not ordaining Blacks was in error and was to cease.

Sadly, a body of writing and speaking had grown to justify the practice. The authors of those writings had to pretty much take it back and admit their errant understanding. A handful of people had become so invested in justifying the practice, that its end caused some cognitive dissonance, and they left the church. Ah, well. It's hard to be humble.