Metallurgy is the study of metallic substance. In terms of Warriors an warfare metal has often been the preferred material for armor and and weapons over more organic materials such as leather or wood. Two metals in particular, Bronze and Iron, had such a significant impact on human history, that they have been used as bench marks for human technological development, With the Bronze Age, coming after the Stone Age and the Iron Age following afterwords.
Metal armor and weapons are generally superior to there more "organic" counter-parts. Metal armor offer better protection and will generally last longer, and metal weapons are generally more effective than wooden or stone ones, being both tougher and capable of doing more damage.
The Bronze Age happened after the stone age, and is where Bronze started to see wide spread use in both military and artistic applications. The Bronze age did not happen every where at once, The earliest a rival of wide use of Bronze was in the Middle east, with India and Europe (generally around 3300 BC at the earliest known areas) following shortly after words and Eastern Asia after that (around 3000 BC at the earliest). While Bronze was the metal of choice during this time, Iron was seeing limited use at this time as well, but not in the large quantity it would later see. The collapse of the Bronze Age is generally accepted to of ended not to the ineffectiveness of Bronze but the cut off of the materials used to make it. Unlike Iron Bronze is not naturally occurring and is made by alloying Copper and Tin, and cut off of trading material cut off the ability to make Bronze.
The Iron is the time when Iron and Steel started being widely used. Like the Bronze Age the Iron age came earlier in Europe, Middle East and India than in more eastern Asia, around 1300 BC as compared to 600 BC. Iron had been used in small degree during the Bronze Age, but early Iron is actually inferior to Bronze however Iron working eventually lead to Steel, which is superior to Bronze. Iron chief advantage over Bronze is exists naturally and doesn't have to be created by alloying it with other metals.