Question

Why did the Mormon faith come under new attack while they were settled in Nauvoo, Illinois? Why did the Mormons eventually leave?

Answer 1

as a morman or member of the church of Jesus Christ and latter day saints i can tell you

in nauvoo is where Joseph smith was teaching the word of god and some people did not like that he was there so they tared and feathered him but they still did not leave but when he had a talk with God through prayer he said go to Missouri 

so the answer  is Joseph was preaching and the other people did not like it and god said to leave

Answer 2

Answer:

Some area residents soon became troubled over Nauvoo becoming a safe haven for thieves and robbers, its booming size, and great economic and political power, some of whom claimed membership in the Mormon faith.

Explanation:

By 1844, Nauvoo's population topped 10,000, with construction being the major industry. As with all large towns, particularly those on the edge of the frontier, Nauvoo attracted many less desirable people, some of whom claimed membership in the Mormon faith. In the spring of 1844 some of Joseph Smith's most trusted followers broke from him, and determined to expose his secret practice of polygamy and break up the political influence of Nauvoo on state politics.

Joseph Smith, as mayor of Nauvoo, declared martial law within the city, preventing armed men from going out or coming in to town. On 24 of June Joseph Smith and a few of the council members surrendered themselves, bugt 3 days later a group of Warsaw militia killed him.

After Joseph Smith's death, the Mormons were persecuted until finally on  the spring and summer of 1846 they left the city,