Why it is legal to carry a gun but not a sword?

Generally in United States, knives or sword are seen as weapons of betrayal, steal and aggression and they are easy to buy, so they are considered to be associated with cheap groups while on the other hand guns are seen as a weapon for self defense, and they are expensive to which make them seen as weapons of upper class white citizens. There is also a history story about guns and swords in US, which you can see at ChicagoGunCase.com " Case Filings.