The helmet most commonly associated with the conquistadors was the morion, a heavy steel helm with a pronounced crest or comb on top and sweeping sides that came to points on either end. Some infantrymen preferred a salade, a full-faced helmet that looks a little like a steel ski mask. In its most basic form, it is a bullet-shaped helm with a large T in front for the eyes, nose and mouth. A cabasset helmet was much simpler: it is a large steel cap that covers the head from the ears up: stylish ones would have an elongated dome like the pointy end of an almond.
Most conquistadors wore a full set of armor which consisted of a heavy breastplate, arm and leg greaves, a metal skirt and protection for the neck and throat called a gorget. Even parts of the body such as elbows and shoulders, which require movement, were protected by a series of overlapping plates, meaning that there were very few vulnerable spots on a fully armored conquistador. A full suit of metal armor weighed about sixty pounds and the weight was well-distributed over the body, allowing it to be worn for long periods of time without causing much fatigue. It generally included even armored boots and gloves or gauntlets.
Later in the conquest, as conquistadors realized that full suits of armor were overkill in the New World, some of them switched to lighter chainmail, which was just as effective. Some even abandoned metal armor entirely, wearing escuapil, a sort of padded leather or cloth armor adapted from the armor worn by Aztec warriors.
Large, heavy shields were not necessary in the conquest, although many conquistadors used a buckler, or small, round or oval shield usually of wood or metal covered with leather.
The natives had no answer for these weapons and armor. At the time of the conquest, most native cultures in North and South America were somewhere between the Stone Age and the Bronze Age in terms of their weaponry. Most footsoldiers carried heavy clubs or maces, some with stone or bronze heads. Some had rudimentary stone axes or clubs with spikes coming out of the end. These weapons could batter and bruise Spanish conquistadors, but only rarely did any serious damage through the heavy armor. Aztec warriors occasionally had a macuahuitl, a wooden sword with jagged obsidian shards set in the sides: it was a lethal weapon, but still no match for steel.
The natives had some better luck with missile weapons. In South America, some cultures developed bows and arrows, although they were rarely able to pierce armor. Other cultures used a sort of sling to hurl a stone with great force. Aztec warriors used the atlatl, a device used to hurl javelins or darts at great velocity.
Native cultures wore elaborate, beautiful armor. The Aztecs had warrior societies, the most notable of which were the feared Eagle and Jaguar warriors. These men would dress in Jaguar skins or eagle feathers and were very brave warriors. The Incas wore quilted or padded armor and used shields and helmets made of wood or bronze. Native armor was generally intended to intimidate as much as protect: it was often very colorful and beautiful. Nevertheless, eagle feathers provide no protection from a steel sword and native armor was of very little use in combat with conquistadors.
The conquest of the Americas proves decisively the advantage of advanced armor and weaponry in any conflict. The Aztecs and Incas numbered in the millions, yet were defeated by Spanish forces numbering in the hundreds. A heavily armored conquistador could slay dozens of foes in a single engagement without receiving a serious wound. Horses were another advantage that the natives could not counter.
It’s inaccurate to say that the success of the Spanish conquest was solely due to superior arms and armor, however: the Spanish were greatly aided by diseases previously unknown to that part of the world: millions died of illnesses such as smallpox. There was also a great deal of luck involved: for example, they invaded the Inca Empire at a time of great crisis, as a brutal civil war between brothers Huascar and Atahualpa was just ending when the Spanish arrived in 1532.
Hemming, John. The Conquest of the Inca London: Pan Books, 2004 (original 1970).