Complex sentence: Scarce wartime resources were used to train and maintain cavalry regiments that were rarely used, and the continued use of the cavalry charge as a tactical maneuver resulted in the loss of many troops and horses in fruitless attacks against enemy machine guns.
Split into simpler sentences: Scarce wartime resources were used to train and maintain cavalry regiments that were rarely used. The continued use of the cavalry charge as a tactical maneuver resulted in the loss of many troops and horses in fruitless attacks against enemy machine guns.