WOW!! I thought I was the only Mormon on this site. That's awesome!
That makes three of us.
Actually, I'm not sure that the abandonment of Polygamy was mainly a question of respecting the law. After all, it was just as illegal most places during the previous fifty years that we'd been practising it, though the matter hadn't got to the Supreme Court, so maybe could be considered still "open" in some sense.
It was basically the fact that our position was ceasing to be tenable. Not only was the Federal Government getting tougher, but the economics of it were getting worse. Since the transcontinental railroad reached Utah in 1869, there had been an increasing flow of eastern manufactures into Utah, not necessities of life, but little semi-luxuries which a husband could buy for one wife, but not for several. So by the 1880s, being a plural wife essentially meant embracing a life of genteel (and sometimes not so genteel) poverty. The result was predictable. By the 1880s, only about half as many plural marriages were being solemnised as in the 1860s.
As a result, Polygamy was getting increasingly marginalised. Polygamists still dominated the leadership, but among the "rank and file", where it had always been a minority practice, it was becoming a steadily smaller one, and this threatened the Church's unity. Many Saints were increasingly unenthusiastic about getting all this hassle for the sake of something they themselves didn't practice. The writing was on the wall by about 1885, when a draft State Constitution, including a prohibition of Polygamy, won a "yes" vote not only in the Territory as a whole, but even in solidly Mormon counties. President Woodruff, who was nobody's fool, got the message, and sought the Lord's guidance as to what it meant, and the 1890 Manifesto duly followed.
Earlier, Polygamy had been a unifying force. As the leading figures of the Church were largely polygamists, they had to stick together. If you quarrelled with Brigham Young, you had nowhere to go. You couldn't just go back to Illinois with your seven wives in tow. As a result, internal splits like the one at Kirtland became much less likely. By 1890, though, it had turned from a unifying force into a divisive one , and so had outlived its usefulness.