Lajos Kossuth is a nearly forgotten name nowadays, but he was quite a figure in the United States of the 1850s. After the 1848 democracy uprisings against the central European monarchies failed, many freedom-minded activists fled to America to continue the fight. Here, often misidentified as "dutch" they would emphatically take the Union side, being largely intellectuals with a social protestant background they were fiercely abolitionist, and were the blazing kernel, the fiery origins of the later US socialist movements that would bring universal education, the hospitals of the "Sanitation Commission" , and Union Organizing to fruition on American Soil. Kossuth was a great orator for principles of freedom and democracy, and Daniel Webster was taken enough to write his biography.
In the years immediately following the Mexican-American war the small army officer corps was well read, and familiar with european affairs, many were stationed in small, nearly microscopic units of the far west, where they spent a lot of time in the field, under canvas, and quite disenchanted with the army's poor uniform choices of near napoleonic frippery. They began to improvise alternatives, along with gum coats, high boots, and revolvers, one common alteration was the adoption of a hat similar in style to Kossouths famous austrian jager slouch hat. This would be formalized by Jefferson Davis as army secretary in the Army's adoption of the Hardee hat, a formalized tall flat brimmed model.
this felt monstrosity, in typical army fashion, Turned the imminantly practical headcover into a travesty of itself, tall, unbalanced, heavy, pinned with brass eagles, ostritch feathers, gold bullion cords, it was hated. Thus it went out the window in favor of the kepi for most units in the field...but for others, unsupplied with the kepi, it quickly underwent field stripping, it's cheap felt did not keep shape in a wet campaign season anyway, so by 1862 it was hard to find an issued one not "punched up" into a mountain, or "pinched" into a cowboy hat like crease to drain rainwater off, and all or most decorations removed, by war's end the exegiencies of multiple suppliers, commissary graft, and make-do ingenuity had brought many variations of the slouch campaign hat, evolved from the jeff davis model. (And the origin of the "Cowboy Hat")
Post war the army settled on the model produced by stetson, and in 1889 new regulations brought about the Rough Riders style with the trench like pinch to shed rain as quicly as possible, big vents to keep the head cool, and a nice wide brim.
This very hat; https://www.ebay.com/itm/Unique-Span-Am-War-Diary-Slouch-Hat-Company-H-Lots-of-Penciled-Art-/363626488711?&_trksid=p2056016.l4276
after the turn of the century it would recieve one further modification; the "Montana Pinch" , a lemonsqueezer like four finger pinch, now iconic as the smoky bear hat, the WWI doughboy hat, still worn by drill sergeants and park rangers.