Omni 1:12-19 

Mosiah discovers the people of "Zarah-emla", who came from Jerusalem in the days of Zedekiah—Mosiah is made king over them—  (Overview Video)

Behold, I will speak unto you somewhat concerning Mosiah I, who was made king over the land of Zarahemla; for behold, he being warned of the Lord that he should flee out of the land of Nephi, and as many as would hearken unto the voice of the Lord should also depart out of the land with him, into the wilderness— Adobe Voice

And it came to pass that he did according as the Lord had commanded him. And they departed out of the land into the wilderness, as many as would hearken unto the voice of the Lord; and they were led by many preachings and prophesyings. And they were admonished continually by the word of God; and they were led by the power of his arm, through the wilderness until they came down into the land which is called the land of Zarahemla.

And they discovered a people, who were called the people of "Zarah-emla". Now, there was great rejoicing among the people of Zarahemla; and also Zarahemla did rejoice exceedingly, because the Lord had sent the people of Mosiah with the plates of brass which contained the record of the Jews.

 Behold, it came to pass that Mosiah discovered that the people of Zarahemla came out from Jerusalem at the time that Zedekiah, king of Judah, was carried away captive into Babylon.

And they journeyed in the wilderness, and were brought by the hand of the Lord across the great waters, into the land where Mosiah discovered them; and they had dwelt there from that time forth.

And at the time that Mosiah discovered them, they had become exceedingly numerous. Nevertheless, they had had many wars and serious contentions, and had fallen by the sword from time to time; and their language had become corrupted; and they had brought no records [just relics] with them; and they denied the being of their Creator; and Mosiah, nor the people of Mosiah, could understand them [language difference].

But it came to pass that Mosiah caused that they should be taught in his language. And it came to pass that after they were taught in the language of Mosiah, Zarahemla gave a genealogy of his fathers, according to his memory; and they are written, but not in these plates.

 And it came to pass that the people of Zarahemla, and of Mosiah, did unite together; and Mosiah was appointed to be their king. 

Genesis 38:30 

27 And it came to pass in the time of her travail, that, behold, twins were in her (Tamar) womb.

28 And it came to pass, when she travailed, that the one put out his hand: and the midwife took and bound upon his hand a scarlet thread, saying, This came out first.

29 And it came to pass, as he drew back his hand, that, behold, his brother came out: and she said, How hast thou broken forth? this breach be upon thee: therefore his name was called Pharez.

30 And afterward came out his brother, that had the scarlet thread upon his hand: and his name was called Zarah.

"King men" had a legitimate claim... 

The Messiah can NOT come unless there is a rightful "King of Judah" sitting upon "the throne of David"

It was not WRONG,  it was arguably legitimate, it was ill timed.  

This is why the "king-men" start basically every war for 60+ chaptes in the Book of Alma.