The sword is an almost universal weapon for every warrior culture around the world, rising to prominence on almost every continent except for the America's, but were particularly used in Europe and Asia. The sword evolved from early knives. Early swords were made of bronze and were relatively short. As iron and steel become prominent swords were able to be made stronger and hence longer. In most cultures the sword is highly revered and considered a symbol of status.
There are many types of swords double edge, single edge, straight, curved, single and two-handed. However all swords sword have two of four major characteristics, straight or curved and one handed or two-handed.
Curved swords are generally slashing weapons, with the curve in the blade being able to be drawn across the target easier than a straight sword. If the end of the sword it weighed, like with the Kilij, it can make the cut even more effective. These swords tend to be single edged as the curve makes it hard to use both side of the blade for cutting. However because the curve makes the tip of the blade away for the hilt, they are not especially effective in thrusts and stabs.
Curved swords offer more flexibility compared to straight swords and are more suitable for mounted combat. Curved swords like the Cutlass were preferred by sailors and were widely used in naval combat until modern age. One of the main advantages of curved swords is that these swords require less training to use compared to most straight swords.
Straight swords tended to be more versatile compared to curved swords, but less effective in slashing. The straight blade meant it was harder to slice targets, but it was much easier to thrust and stab. Generally double edged due to the ability to use both sides of the sword equally well. The second edge also made stabs do through soft tissue easier than a single bladed sword.
Straight swords are more versatile compared to curved swords but are less suitable for mounted combat. Straight swords from Renaissance and later ages, like the Rapier or the Colichemarde sword, were optimized for thrusting, dismounted and anti-sabre combat. However these swords were primarily dueling weapons and never saw widespread use on the battlefield.
A sword being used in one hand has several advantages over a sword being used in two hands. The sword being used in one hand is generally capable of hitting faster than a two handed sword, and gives the user more of a reach than their opponent, given the two swords are equal length. Another big advantage is that the other hand can be left open allowing it to hold something else, it could be a shield, another sword, a hand axe, a dagger or even a a small fire arm. However this technique has a major weakness, a single handed sword is much easier to deflect than a two-handed sword and doesn't carry much strength. One handed swords are ideal for mounted combat.
Two handed swords have several advantages over the one handed. Because they are designed to be used with both hands, they can be made longer and heavier. This allowed for a the weapon to hit with greater force and weight. Even if the sword isn't very long, a two handed technique still allows the user to put more strength into an attack than a single handed sword. Because both hands are used, the weapon allows the user to to exert more leverage on the opponents weapon than a single handed sword. Large two handed swords, like the Claymore, effectively increases the reach of the wielder in a sword fight. However when using both hands, the user can't use another weapon or shield, like with an one handed sword. Another disadvantage is that two handed swords can not be used from horseback.
The biggest advantage of the any sword is it's versatility compared to other weapons. Most swords can stab, slash and, hack the enemy, giving cutting damage, piercing damage and blunt force trauma all in one weapon. As opposed to a spear, club or ax, which are only capable of a few options. Additionally, a sword is generally more capable of parrying incoming attacks on it's own.
Swords are generally more expensive than other weapons, taking a skilled hand to make them well. Additionally in order to use properly most swords require a great deal of training. In some cultures only nobles or warriors were allowed to carry these weapons. Also generally speaking most swords don't work well against any form of armor, especially Plate armor. It should be noted that one of the reasons the sword evolved into a narrow thrust oriented blade is believed to be the fact that such a thrusting style was indeed very effective against most armor.
In the show many warriors use swords. In the final fight, if both warriors have swords, the fight almost always comes down to a sword duel.