Western influences on China's military

Iron use appeared to sprung out spontaneously, and when you have iron and carbon, you will inevitably discover steel one way or another. But China appeared to be quite ahead in a number of innovations, including the use of blast furnaces, differential heat treatment, forging and lamination (folding multiple layers). At a time when the rest of the world were using wrought iron fo their swords (Roman gladius for example), Han armies began brandishing dao that was forged, laminated and folded steel, a sword making process still preserved in Japanese sword making.

Jian to Dao transition was a result of moving from infantry to cavalry army, moving away from infantry close formation stabbing, to on the horse slashing---or slashing at the horse. This also comes with the appearance of two handed swordmanship styles.

When you can melt iron and carbon together with low temperature, you get wrought iron, which has bearly no carbon and very soft. If you melt them with high temperature, you get pig iron (where did this name come from?) which has quite some carbon and very fragile. The amount of carbon in steel is in between. So you either put more carbon into wrought iron or extract carbon from pig iron to produce steel. In reality you have to produce pig iron in order to get steel, so you at least need the technique to reach high temparature. China developed various techniques to extract carbon from pig iron, basicly first by melt pig iron together with iron ore, then the technique advanced to melt pig iron and wrought iron together. By this way, raw steel can be produced in large amount. Then use multiple layer forging, heat treatment etc. to produce fine steel. China also had the techniques to attach blades made by fine steel to body made by raw steel. Therefore mass production of good sword could be achieved in big plants.

If someone knows something about Romance of the three kingdoms, he can never forgot the hero Ma Chao. Ever a roman troops survived in their war towards Persia, and they settled in China when it was Han-dynasty. Ma Chao war believed to take the advantage of the roman troops, Especially the use of spear. Thanks to the combination of the western and eastern, Ma's troops were invincible.