Longswords were favoured pretty much everywhere because, beyond the simple status symbol of being able to afford one long piece of metal (which at one point meant you were hella rich) and being part of the warrior caste, they offer versatility.
They can give you some reach (for example, enough reach to never let guys with small machetes/daggers close up ). In tighter quarters you can grab them at half-blade and still fight just fine. You can use them one handed or two handed. They can slash. They can poke. You can use the pommel+crossguard as a striking weapon by grabbing them the wrong" way around (yes, it was done), or even the right way around and “pommel whipping” the guy.
They’re fast, they’re not too cumbersome to carry, their strikes don’t leave you as open as those of an unbalanced axe or hammer and you can redirect a strike mid-way through with only a flick of the wrist. You can use them to deflect blows too. You can use them in a duel, or in a tight unit, on horse or foot, with or without a shield.
They look cool. They make that “schwing” sound when you pull them out of their scabbard, too :D.
But **magnusblitz **is right than in many non-Ancient cases the longsword was the “backup” weapon, as well as the “peace” weapon (i.e. the one you keep on your person at all times because status+self-defence). On the open field, medieval knights had their lances and getting stuck in the melee was a bad idea ; infantry their spears/greataxes/pikes/halberds/whathaveyou because those tend to work better in a cohesive unit.
Remember though that from the ~Xth century onwards, in western Europe at least, field battles became the exception rather than the rule owing to all them castles dotting the landscape.
[QUOTE=the_diego]
The primary offensive weapon by then was the javelin, though the sword usually settled it at the end.
[/QUOTE]
Nah, the skirmishers and pila-throwing legionnaires were there to soften up the enemy line, make a few holes here and there that the charge could exploit and maybe threaten the other guys’ skirmishers with. The bulk of the fighting was a choreographed ballet of shieldbump, push, PUSH DAMMIT, stab as required, repeat. Then move back to let the second line have its fun.