Because they wanted to get rid of him and they were trumping up all sorts of stupid charges and stuff to do so. It's rather interesting how they could never get any charges to stick. It's hard to do that when the person is totally innocent of any crime.
Why was he tar and feathered 3 times? Whe were Mormons raped, killed, and beaten? Why was it legal to kill a Mormon and steal all his property until 1972 in MO? Why was a mob allowed to enter the jail and shoot and kill Joseph Smith and his brother who had NEVER been convicted of a single crime?
All these have pretty much the same answer. MO, IL, NY, and OH should be rather ashamed of their history.
There's a lot of revisionism and lies out there about what really happened. RARELY is it reported that Joseph Smith shot and killed two men. It's not in kipped of other sources. Not one Mormon site I looked through had the account of Joseph Smith shooting and killing anyone or jumping out a window to his death. In fact, they say he was murdered by a mob of people but he died jumping out a window to his death trying to escape after shooting three men and killing two of them. http://www.i4m.com/think/history/carthage-jail-smith.htm
Why do you think he was charged with treason?
This was an evil man who had over thirty marriages. He married other men's wives. He married teenage girls. He was and is and will forever be a false prophet. He was charged with so many things it's hard to know where to begin....
He incited all sorts of riots...was charged with false money making schemes in many states (and convicted) and even charged with adultery...
he was "charge of "treason" for declaring martial law and ordering out the Nauvoo militia to keep peace"
He abused his position of power and tried to clamp down on those who knew he was a liar and fraud who kept charging him with his crimes!
The actually verifiable answer is this. Joseph Smith was engaged in polygamy, and had started to take women who were already married to living men as his wives. He made several proposals to Jane Law (wife of William Law) who spurned his advances. After being pressured so much by Joseph, William and Jane left the Mormon church, and started a newspaper named the Nauvoo Expositor. The one and only issue it printed was very critical of Joseph Smith and exposed many of the secret, and horrible things he was doing. In response to the issue, Joseph ordered the printing press of the Nauvoo Expositor to be destroyed. Obviously this was an illegal order since we live in a free country that promises a freedom of the press. Joseph was rightfully arrested on charges of treason, and taken to the Carthage Jail, where he was assassinated.
He was persecuted? Do Mormons think Warren Jeffs is in jail because he is persecuted too?
Both were totally oblivious to the authority of other powers over them. Neither thought they had to follow the law.
Joseph Smith was never persecuted because of his theology. He was hated and prosecuted because of his bad behavior, including polygamy and lying about it.
In fact, when the people of one state tired of his behavior, the people of the next state would welcome him, thinking he had been persecuted. They knew his theology. It didn't bother them when he came, nor when they drove the Mormons out. So the Mormons went across New England and the Mid West from state to state.
Theology was never the issue.
The issue was block voting to grab power, land speculation, illegal banks, large armies, appointing himself King, General, etc. Oh, and getting a special deal for Nauvoo where in Mormons could raid the countryside but could only be prosecuted by Mormons in Nauvoo - leaving them free to harass the locals without recourse.
Today Mormons send endless annoying missionaries, flex their political muscles, and then ask in bewilderment why people don't like them. They never look objectively at their own bad behavior and the impact it has on others. Some things never change.
There are no records of Mormons killed that come close to the known dead from Mountain Meadows Massacre.
He was charged by treason by Governor Ford to placate the mob at Carthage, because what laws they had couldn't keep Joseph Smith in Jail. So they made up treason.