Split where I thought best, feel free to tweak if you disagree
ditto for the first of '1864-1865'
Split where I thought the most logical break was
" Battle of Fort Sumter; events in the state of Missouri led to an expansion of the war into that state" I don't think these are great bounded by a semicolon because 1) it's not immediately clear where Sumter is (to a passing reader) and 2) it's not clear when the war expanded into Missouri, would recommend clarifying both and splitting into two sentences
I've taken a crack at this, is this better?
" against the Red River campaign" our article refers to a 'Red River Campaign' with capital C
"where the important" I don't think 'important' is needed here
Removed
"On October 27, the battalion," wants a year (Even though the year is in the subsection)
My instinct is that since this is a continuation of the formation narrative from the last paragraph of the previous section, this isn't needed. If you really think it is, I can add one.
"but Parsons right" I think you're missing an apostrophe here?
Good catch
"Mitchell's unit had taken 450 men into Prairie Grove; 20 of them became casaulties" seems to be a very roundabout way of saying "20 of the 450 men in Mitchell's unit became casualties" but I'm not positive my phrasing is better
I don't like beginning sentences with numbers, since there's great debate in some circles if it's okay to start with a numberal, and
MOS:NUMERAL would want 20 here, not twenty. Thinking of a solution here
"Either way, Mitchell's regiment was given the designation of 8th Missouri Infantry Regiment on July 23, by the
Confederate States War Department" I like "On July 23 the
Confederate States War Department designated Mitchell's regiment as the 8th Missouri Infantry Regiment" better personally, but its really your choice here"
Went with something similar to your suggestion, tweaked to avoid close paraphrasing.
"Major General
Frederick Steele" clarify whether he's Union or Confederate pls
Done
" but slid his army around the end of them" what does this mean?
Just stated outflanked, why I didn't write that in the first place, I don't know
" By the latter half of March" I think you want "later" or "second" though I guess latter isn't technically incorrect
Went with second. Stylistically, I would prefer latter, but since it's a bit of an odd construction here, I've changed it
"had lost all confidence" is all really needed here?
Nixed
"Some of the subordinate Union officers had lost all confidence in Banks earlier in the campaign, including one who briefly entertained ideas of a
mutiny. This contributed to the Union decision to retreat" I'd suggest "The decision was in part because some of the subordinate Union officers had lost all confidence in Banks earlier in the campaign, including one who briefly entertained ideas of a
mutiny." or something
How does "This decision was made in part because some of the subordinate Union officers had lost confidence in Banks earlier in the campaign; one had even briefly entertained ideas of a
mutiny" sound?