This old answer is narrowly focused, looking just at the failure of the US Camel Corps, but might be of interest.
Equine military history in the 20th century is my specialty. Both horses and camels were used in warfare during the 20th century, sometimes in the same places.
Camels survive better in hot, tough climates but horses do better in moderate climates. Horses were also simply a lot more readily available. There's also the issue of trainability and speed/fighting mobility.
Some resources:
"Camels and Colonial Armies: The Logistics if Warfare in Central Asia in the Early 19th Century," Journal of the Economic and Social History of the Orient, Alexander Morrison, Sept 2014.
Animal Labor and Colonial Warfare, James L. Hevia.
Britain Goes to War, Ed Peter Liddle (pop history more so but discusses differences between camels and horses in WWI)
Trenches and camels: Australian recollections of Gallipoli and the Imperial Camel Corps... Oliver Hogue.
Sorry for the lack of breadth in my answer, unfortunately I'm not educated enough on camels historically or biologically to offer more.