[wnewman]

"Transporting goods inland was hard because..."

I think it should be something like "was even harder than you would think because..." Sure it was harder before efficient harnesses, but even after efficient harnesses were invented, indeed even in good terrain, horses and carts were very expensive. Note that not only were railroads and trucks a lasting revolution in commerce, they were a radical improvement on another (less enduring) radical improvement before that, extensive artificial canals (very famously the Erie Canal, but there were many others, some successful). Rivers and canals were central to inland commerce in Europe and America because even with good harnesses, enthusiastic breeding of suitable strains of horses, and various other refinements horses and carts are still expensive per ton per mile.