Short answers, pulled from the story.
The four core components that define how fighting forces operate on a battlefield are kinetic or firepower function, mobility, protection, and shock action. Kinetic effects were delivered by clubs, spears, javelins, and bows until artillery arrived with the Romans.
Full tactical mobility was not achieved until World War II when armoured and motorised formations succeeded. Tactical mobility remained restricted until the latter years of World War I before tanks improved movement sufficiently to allow decisive tactical manoeuvre.
Personal armour has been worn since the classical period to provide individual protection measures but had been largely discarded from battlefields by the 18th and 19th centuries. Helmets returned during World War I in response to artillery firepower threats while body armour returned for infantry particularly in Western armies following World War II.
Tom Wintringham proposed six chronological periods where the first unarmoured period lasted until the Battle of Plataea in 479 BC and the second unarmoured period ended at Pavia in 774. The third unarmoured period ended at Cambrai in 1917 when infantry with steadily increasing firepower became predominant.
Operation Market Garden in September 1944 demonstrated limitations of vertical envelopment strategies despite heavy losses. Parachute and glider operations provided significant mobility to ground forces but reduced tactical utility once troops landed due to challenges persisting today as armies continue integrating aviation into their operational doctrines.