I've just started listening to the Fall of Civilizations podcast (https://fallofcivilizationspodcast.com/), and their second episode is on the Late Bronze Age collapse. The theory they put forward as to one of the reasons the big successful Bronze age civilizations got out-competed is that bronze is very expensive / hard to acquire, primarily because of the need for tin. (Copper is very common but unsuitable for weaponry without turning it into bronze.)
Iron is extremely common and cheap, but requires much much higher temperatures to work with than bronze. Once the furnace technology was out there to make smelting iron and creation of steel feasible, poorer / less complicated civilizations were able to make iron weaponry and go up against their richer neighbors.
Bronze is superior to iron, but not to steel. Both bronze and steel can take very sharp edges while only steel can be tempered to be springy and tough and therefore can make much lighter weapons. Iron is soft, weak, prone to rusting, can't easily take or hold an edge, and requires a lot of fuel to process from ore, but you can get it anywhere in large quantities if you have the fuel, while bronze needs the much harder to find tin.
Depends on the quality of the iron. Poor quality iron is often inferior, but of course actual steel is much better. Bronze can take a great edge but is a a bit softer and can get edge damage in battle/usage quicker. However bronze does have one big benefit over iron/steel, repairability. If a bronze item is damaged it can be cold worked and annealed repeatedly over a simple wood fire. With iron or steel you need a more proper forge and charcoal to repair it and it has to be worked while hot which requires more tools on hand to do properly. A "cheap" bronze sword can be smashed over dozens of heads until it is basically a bronze club, but then later with a campfire and some rocks or simple hammer can be reworked and sharpened into a sword again.
Any real difference in damage would be weight based, as swords were more used for beating than cutting. It's likely that one metal could hold a better edge, and one (perhaps the same) would be more resilient to breaking.
It's not quite like the D&D "this metal is higher ranking and does more damage".
I think they are comparable. A blow from a bronze sword will kill you just as well as a blow from an iron sword. The most widespread weapon of all times prior to the American Revolutionary War and the Napoleonic wars were spears. A spear with a bronze tip and one with an iron tip will also kill you with equal probability. If you have a shield, the damage to the spear is much more likely to come from a broken shaft than from a cracked tip. The shield itself generally had a metallic part (a "boss") that could be made of bronze or iron. Both were equally effective.
Swords were generally not used in battle. But if used, a bronze sword was a bit more likely to crack than an iron sword. Bronze weapons were resistant to corrosion though. So that meant they did a better job in their secondary role: that of provider of status. A warrior with shiny armor, shield and sword is much more imposing and frightening than one with a rusty armor, shield and sword. Of course, in the bronze age, war was more ritualistic than war during the Roman empire, when war was much more like an industrial operation. For the purposes of the Roman empire, iron was probably doing a better job than bronze.
People often compare sword with handguns. Handguns nowadays are deadly weapons, but they are not used in war, where people use assault rifles instead, or other heavier weapons. Swords were sidearms. Warriors carried them around every day, they could be used for self defense (in those times there was not police or law enforcement). Or they could be used for intimidating opponents, and if needed, for chopping someone's head or limb.
In combat though, spears were much, much more effective.
With one exception. As far as I can tell only one exception, but a big one. The Romans have figured out that all other people are quite bad at close quarters combat. Since soldiers were used to using spears, very few soldiers knew what to do if someone got in a close range than the length of a spear. The Romans then would bull-rush the enemy using their shield, and when close they would use their (quite short) swords. Without training, their opponents didn't stand a chance. Of course, this type of battle tactic required an enormous amount of training. The Romans did that because they were a very war-oriented society. Others couldn't match their level of training.
Even for the Romans though, who were regularly using swords, the choice of bronze versus iron would have made little difference. Although bronze is a bit more brittle than iron, and a bronze sword is more likely to break when it strikes a hard object, the Romans were trained to thrust the sword, not to use slashing moves. Thrusting is much more deadly, but less instinctive. It's another thing that requires extensive training, which the Romans were great at. For thrusting, I think a bronze and an iron sword do equally well.
Nice explanation, but the Romans did use spears - the 7-foot heavy pilum. They just threw them. It was effectively used to disrupt a threat in a mass volley before swords were drawn and the zerg rugh. Several battles were won by the pilum - the battle of Telamon for example.
I was under the impression that iron causes more damage- hence, why the Iron Age followed the Bronze Age, because the people with the iron armor and swords would pierce through the armor of the peoples wearing the bronze armor, but not vice-versa.
