The face of warfare is constantly changing. The basic see-saw is between Cavalry and Artillery on one side -- armaments that require large, central authorities to purchase (armored knights, chariots, seige engines, tanks, missiles, bombers, etc.), and Infantry on the other -- armaments that are more "democratic", that can be purchased and employed by "yeomen" (longbows, rifles, swords, RPGs, etc.).
Between Crecy and WWI, Infantry, armed with the longbow, then the rifle, dominated the battlefield. Since WWI, Cavalry and Artillery (bombers and missiles are essentially long-range artillery) have dominated the battlefield. Some will put the fulcrum as late as WWII and some will put it as early as the War of Defense against Northern Agression
Better RPGs (to defeat tanks) and low-cost stand-off delivery systems (to replace Artillery) could tilt the balance back to Infantry.