Root of Italian Disunity after Roman Collapse?

[Valmy]

And plenty of civil war in between.

Yeah the Italian cities did not really factor in until those city walls started to be built.

[Valmy]

Eh, it more a war against an overbearing ally.  The Italian states were nominally independent, but they lost a great deal of power to Rome.  Rome pacified some of their allies with offers of citizenship (which further eroded those states power), but not all of them.

Um no the war was because they kept being denied Roman Citizenship.  The Italian state they developed was almost entirely identical to the Roman Constitution.  The only Italian peoples who wanted more than that were the Samnites.  And even then they fought largley on the Marian side against Sulla and his allies.

[Siege]

Two inventions: Crossbows and gunpowder, mixed with the ability of city-states to support small but professional armies through trade profits.

I don't see why gunpowder promotes the independence of city states. Rather the opposite, I should think.

Crossbows and gunpowder weapons are far easier to learn to use than bows and swords.
They allowed city militias to defeat feudal armies made of knights and bowmen that needed a lifetime of training to be good at their trade.
Later on, allowed the free companies to hire dudes out of anywhere, with no training, and making them into an effective mercenary force.

[crazy canuck]

Siege, I think the point you are missing is that gunpowder is useful at blowing down city walls making the defence of said city more difficult - no matter how many crossbowmen one has hired as mercenaries.

[Razgovory]

Crossbows and gunpowder weapons are far easier to learn to use than bows and swords.
They allowed city militias to defeat feudal armies made of knights and bowmen that needed a lifetime of training to be good at their trade.
Later on, allowed the free companies to hire dudes out of anywhere, with no training, and making them into an effective mercenary force.

Massed armies came later not because of technology, but because of money.  A feudal army was cheap.  You paid them in land and then they buy their own equipment and train themselves.  It was good in the dark ages and early middle ages because money was so scarce.  Mercenary armies came about in the later Middle ages because of the rise of cities.  Cities produced real money that could be used to pay for soldiers.  Mercenary armies were often more reliable then feudal armies (these mercenary armies weren't always free lance and many were more like modern volunteer armies.  But they normally fought for money rather then loyalty.  Still the distinction between mercenary regiments, feudal levies, and early modern military formations was fuzzy).

[The Minsky Moment]

Implicit in the question is the false assumption that a unified national state is the natural or default form of political organization and that any deviation requires special explanation.  The city-states thrived because they were viable and successful forms of political organization that satisfied peoples' needs. 

[Malthus]

Implicit in the question is the false assumption that a unified national state is the natural or default form of political organization and that any deviation requires special explanation.  The city-states thrived because they were viable and successful forms of political organization that satisfied peoples' needs.

Yup, one may equally ask why Europe "failed" to become united in an empire a la China or Rome.

OTOH, while I agree that the Renaissance achieved spectacular results in terms of art, science, etc., the city-state was unable to avoid predation by early modern states.

Italy suffered invasion after invasion and only succeeded in not being absorbed by one state or another at the cost of playing one state off against another, resulting in Italy commonly being a battlefield.

The pros of having a city-state seem to be rapid advancement in commerce, art, science - essentially, civilization. The cons - lack of security. 

[HVC]

I blame walls and invasions (or threat thereof). For conquering in ye olden days nations were good. You collect a larger army and run roughshod. To defend it's different. Army bypasses yours and you city is defenseless.

[The Minsky Moment]

OTOH, while I agree that the Renaissance achieved spectacular results in terms of art, science, etc., the city-state was unable to avoid predation by early modern states.

While there is truth to that, the story is more nuanced.
First of all, the city-states thrived for centuries during the high and late middle ages.
Second, while they went through some rough times in the late Rennaissance and early modern eras, it's not like the big monarchical "national" states or the empires fared much better.  France suffered horrible, ruinous civil wars.  England had the War of the Roses, a period of subjugation to Spain, and its own nasty civil war.   The German empire and its constituents suffered even more.
The northern city-states continued to survive in modified form as "region-states" for quite a while, up til unification.  Economically they stagnated somewhat but due to the early lead still had higher levels of development than most of Europe well in the 18th century.   Maybe nothing to write home about but not so bad when one considers the fate of Bourbon France and Spain.

[Viking]

I thought it has something to do with the constant invasions from the Ostrogoths to the situation where Italy becomes a playground for Germany and France and later Hapsburg and Valois to fight it out on a small scale.

All attempts at central authority gets destroyed by the invader or corrupted from within by the pope while all invaders fight a faction in disfavor willing to cooperate with the invaders. The histories of all european countries is basically the struggle of the central power to maintain and expand itself, the history of italy and germany is the struggle of minor factions and invaders to destroy the central power.

Byzantines invade and all but destroy the ostrogoths, the ostrogoths revive, the lombards invade and destroy the ostrogoths. Arabs invade and weaken the lombards, the normans invade the south and kill everybody. The pope and emperor fight it out turning imperial lands in the north into city states, crusade cement status quo, large states get stable government, small states get left alone. At that point the early renaissance starts to happen and historians discuss the emergence of the middle class.

[Ideologue]

And plenty of civil war in between.

Yeah the Italian cities did not really factor in until those city walls started to be built.

Indeed.  That's why you keep level 1 forts, especially after history had the patch change to adjust the size of rebel stacks to compensate for larger fortresses.