What a crock of crap! Missouri was split, like the other border states, on the question of secession. While it is true that the state convention voted unanimously not to secede in March 1862, the arsenals that you speak of were federal arsenals and Governor Jackson had no legal right to seize them. So the sending of militia to seize it was illegal. You say that 'feds responded by marching the U.S. army on the state capital to oust the governor and state legislature' which is nonsense, and that 'the state government convened in October in the town of Neosho' which is false. The legislature remained in office, and Claiborne Jackson was impeached and removed from office. It was the impeached governor and the minority of the state senate which met in Neosho and voted secession, something that they lacked the authority to do. So Missouri remained legally in the Union throughout the war, and while she did send men to fight on both sides the majority fought for the Union.
It had decided to stay in the union and proclaimed its neutrality.
While it is true that the state convention voted unanimously not to secede in March 1862, the arsenals that you speak of were federal arsenals and Governor Jackson had no legal right to seize them.
Jackson didn't seize the St Louis arsenal though! The militia was assembled near St. Louis to prevent the use of the weapons against the state of Missouri and was ready to act in the event that the federals waged war there, but at the time they were captured they had not done anything. They were simply assembled as the legislature and governor had approved them to be! This event is widely attributed to the overzealousness of the union commander, Nathaniel Lyon.
You say that 'feds responded by marching the U.S. army on the state capital to oust the governor and state legislature' which is nonsense
History records that Lyon led a march toward Jefferson City, on June 14, 1861. As they approached and occupied the capital, the governor, lieutenant governor, and a quorum of the state legislature - all duly elected officials of the state - fled to the southwest. The state militia attempted to impede the march at Booneville on the 17th. Another union attempt to incercept the governor was made on July 5th at Carthage, where the militia held off the advances.
and that 'the state government convened in October in the town of Neosho' which is false.
The legislature remained in office, and Claiborne Jackson was impeached and removed from office.
I just did a search for the terms "claiborne fox jackson missouri impeached" and found no hits pertaining to anything of the sort. He was indeed "deposed" by a "provisional government" established by the yankee army, but that "government" lacked elected legitimacy and was established by a military force that pushed out the legitimate government and occupied the capitol.
It was the impeached governor and the minority of the state senate which met in Neosho and voted secession, something that they lacked the authority to do.
Records from Neosho indicate that a quorum of the legislature was present. They were the only legitimately elected government in the state, and Jackson was the legitimately elected governor. Therefore their action was valid.