For much of its history, Italy was a geographic expression. Before its unification in 1861, it was a collection of city states and principalities, frequently a target for foreign powers. Many of these weren't actually monarchies, but republics ruled by a collection of oligarchs. The city states were mostly rich and concentrated (relying on trade and banking) centers of Art and culture and formed the cradle of The Renaissance.
Niccolò Machiavelli lived in and wrote about this period in The Prince and Discourses on Livy.
Some examples are listed below.
You Ain't Nothing But A Hound, Doge: the Most Serene Republic of Venice aka The Venetian Republic (697 - 1797)
This state centered on the city of Venice, but owned mainland territories in the modern-day countries of Greece, Slovenia, Croatia, and Montenegro. Once even ruling Cyprus (the war for which was the backdrop to Othello). Had a large merchant fleet, a powerful navy and controlled a lot of trade to the Middle East for much of its history (including silk, spices, and slaves). Started out as a minor protectorate of the then mighty Byzantine Empire, before becoming a rival, and eventually masterminding its toppling in 1204 by the 4th Crusade. While the resultant Latin Empire didn't last long (being deposed in 1261 by the Byzantine Empire of Nicaea), the restored Empire was far weaker and helped cement Venice's dominance of the Mediterranean.
The city-state was famous for its Murano glass as well as its silk weaving industries, but perhaps the most important industrial site in the city was its arsenal, a shipyard which could churn out hundreds of vessels in a matter of months using early assembly-line techniques which were literally centuries ahead of their time. Of course, the arsenal's production methods were kept as an absolute secret, aided greatly by the fact that it was built on an island which was off-limits to foreigners and even most Venetians.
It was referred to as a "mixed republic", with a monarch-like doge (who lost much of his powers over time, and no, not that one), a Senate and a Major Council made up of key aristocrats, the latter being the real ones in charge of the country.
Venice declined as a major power once alternative routes to the East were found by the Portuguese (especially the route around Africa, at the Cape of Good Hope, achieved during the Conquest of Portuguese India), and as trade and investment flowed towards the Americas and away from the Mediterranean due to the Spanish Empire. The republic fought several wars with the Ottomans, losing often despite occasional hope spots like the Battle of Lepanto, and lost most of their possessions in the Eastern Mediterranean as a result. Even worse, their forceful peace treaties with the Ottomans brought the ire of the Spanish and their Italian allies, which did not make the republic's life easy. By the very end, Venice was degenerating into a gambling center, an association still noticeable in places like Las Vegas or Macao today, although retaining enough power and influence to survive.
Eventually invaded by Napoléon Bonaparte, the Austrians took all its foreign possessions in the 1797 Peace of Leoben. Despite some attempts at rebellion, the Venetians never regained independence and were later absorbed into the unified state of Italy.
A key contribution to the study of European history has traditionally come from Venice, as its the state archives have pretty much all the diplomatic correspondence and ambassadorial reports, containing warts-and-all descriptions of the courts of Europe, their rulers, etc, although more modern historiography has become more perceptive to the reasonable-to-absurd levels of bias found within.
Fun fact: We owe the word "pants" to Venice, sort of. The word derives from the name of a popular stock character in Italian comedies named Pantaleone. The name Pantaleone identified him with Venice due to St. Pantaleone (the name means "all-compassionate") being a popular saint with the Venetians. The comedic figure was a silly old man who wore tight trousers over his skinny legs, leading people to identify the clothing with the character, leading to the term "Pantaloons", which were shortened to "pants" in the 1840s.
Florence (1115 – 1532)
Seen as one of the great centres of the Renaissance (the other being Rome), Florence was the hometown for many, if not most, of the masters of the Renaissance.
Some 200 prior to all of that, the city had been home to Dante Alighieri, who wrote The Divine Comedy in exile, after his faction had won and split into two, after which split Dante ended up on the losing side. This soured him on republics, a detail later Florentines preferred to gloss over.
Much of Florence's reputation came from the generous patronage of the Medici family, bankers who, through well-placed bribes and great shows of wealth and prestige, basically ran the city. Their regime reached its apex under the patronage of Lorenzo the Magnificent. Unfortunately, he died in his prime at 43 years old. His generous patronage — and his failure to uphold the golden rule of medieval banking, that one doesn't lend to kings (because they don't pay one back) — left the bank, well, bankrupt. His son and heir, known to history as Piero the Unfortunate, fled to Venice and sold off the family jewels while begging Florence to take his family back. The city was taken over by the fiery populist monk Savonarola, who did his best to undo everything the Medici had created, with his "Bonfires of the Vanities", in which countless works of art were destroyed as corrupting influences. After the pope, an old friend of Lorenzo's, finally toppled Savonarola, the republic was restored.
They immediately set to commissioning art to glorify their city-state, including Michelangelo's famous David. Leonardo was commission to do a fresco of The Battle of Anghiari, but when he took too long, they hired Michelangelo, his great rival, to do a competing fresco of another, more famous battle — that idea may or may not have come from Niccolò Machiavelli himself. However, it was the Medici who had the last laugh — Lorenzo's second son became Pope Leo X, and a second Medici became Pope Clement VII (the one who denied Henry VIII a divorce from Catherine of Aragon — you know, because Catherine's nephew, Holy Roman Emperor Charles V from the House of Habsburg, had sacked Rome and held him hostage). But Clement did manage to grant his cousin Cosimo de Médici the title of Duke of Florence, turning the republic into essentially a mini-monarchy.
Cosimo allied with Charles V during the Italian Wars, which served him to expand his duchy by conquering Siena in 1555 and purchasing a naval base in Elba from the Genoese, in exchange for handing Charles a chain of strongholds, the State of the Presidi. Afterwards, Pope Pius V elevated Cosimo to Grand Duke of Tuscany, an unprecedented title. The Austrian and Spanish heirs of Charles V weren't amused, as this implied Tuscany was officially leaving their jurisdiction, but relented after Cosimo's successor Ferdinando paid them a hefty compensation. The Great Duchy of Tuscany managed to retain its prestige and stability in midst of the perennially headbutting Italian states, in many ways became more powerful and influential than the Republic of Florence had ever been, even enjoying a brief colony in Brazil, although it lost much of its florid Renaissance aura in the process.
After a failed alliance with France, Ferdinando I returned to the Habsburg orbit, so Tuscany stayed as a sort of Aloof Ally to the Spanish Empire, joining forces in the wars against the Ottomans and even entertaining a new Crusade for Holy Land. They also supported the imperial side during the Thirty Years' War, being among those who called for war to the very end (it's believed they helped murder Albrecht von Wallenstein, who saw the war effort was useless and wanted to make peace). The duchy only started going down at the end of the 17th century when Spain itself did. They partially rebounded with a new dynasty, in this case by merging into the Habsburgs directly, whose Spanish branch had ironically died off around the time.
It is because of Florence's legacy that it was chosen to be the capital of a united Italy in 1865, until the final capture of Rome six years later.
The Republic of Genoa (1096 - 1815)
The other Italian trading republic to survive until the French Revolutionary Wars (Lucca and San Marino were also republics but weren't known for trade). It was originally a four-way thing between Venice, Genoa, Florence and Pisa, but the latter two ended up becoming parts of other monarchies. Placed in Italy's opposite corner and ruled by its own elected Doge, Genoa was naturally The Rival to Venice, leading them to fight a back and a forth series of naval wars during the 13-14th centuries. Although Genoa failed to completely match its rival's prestige, being surrounded by way stronger competition than the remote Venice, it was enormously influential too: not only Christopher Columbus and Amerigo Vespucci came from here, but Genoese traders were the first ones who (inadvertently) first brought the Black Death to Europe from their trade posts and colonies in Crimea, and Genoese mercenaries helped The Fall of Constantinople.
To better reflect its rivalry with Venice, Genoa copied Venice's self-styled title of the "the Most Serene", but later decided it was too lame for them and rarely used it. Instead, Genoa called itself the Darker and Edgier titles of "the Superb" and "the Dominant". Ironically, and unlike what these nicknames imply, Genoa had a reputation to be much easier to work with than the notoriously fickle Venice, if anything because the presence of its powerful neighbors kept its worst antics in check.
Like other examples in this page, Genoa was officially part of the Holy Roman Empire, although in practice it self-governed. This changed in the 14th centuries, where their decline, caused by war against the Venetians, the Aragonese and the Ottomans, landed them under different stages of French and Milanese control. At one point, as France had little maritime tradition, the Genoese became their naval enforcers, albeit rivaling with the main French port of Marseille, which Genoa would have surely loved to see destroyed.
Genoa started a long-lasting, symbiotic relationship with the Spanish Empire in the times of Charles V, who found common interests with Genoese chieftain Andrea Doria and recruited him as his grand admiral. Even after the city's maritime significance gradually decreased, it remained in Spanish orbit as a reliable naval ally, to the point their armadas often functioned as one and the same. More importantly, Genoa also found a new place as Spain's banking center, funding their many wars with large loans either repaid with American gold and silver (much to the European economy's inflation) or not at all (much to the Genoese's disgrace), although generally benefitting enough that historians consider it a small golden age for the republic. The main Genoese families became filthy rich, at one point owning Panama, and produced in exchange several big names of the empire, like the general Ambrogio Spinola and the businessman Ottavio Centurione.
Bound by their Odd Friendship, the republic declined at the same time as the empire, ocasionally butting heads throughout the process. After the tumultous War of the Spanish Succession, which brought them to the orbit of Louis XIV of France and his descendants, Genoa and Spain remained loosely allied, but it would not be the same anymore given that the new political and economic mores meant they had stopped being codependent (Spain didn't need so much money and Genoa didn't need protection against France anymore).
Genoa possessed the island of Corsica for many years, but failed to put down a radical republican independence movement led by Pasquale Paoli - so they gave up and sold the island to France. The French succeeded, but in the process Corsican revolutionary ideas and a certain Corsican named Napoleone Buonaparte spread to France. Of course, the result was The French Revolution, and General Bonaparte who was instrumental in conquering Italy for the French Revolutionaries, who overthrew Genoa, proclaimed a revolutionary Ligurian Republic. After the Congress of Vienna, the region was merged with the Kingdom of Piedmont-Sardinia.
Fun fact: Speaking of pants, jeans derive their name from the city of Genoa. The durable cloth used to make these pants derives from the fabric used by Genoese sailors to cover the goods they stored on the docks.
Savoy (or Piedmont or Sardinia or Piedmont-Sardinia or the lands of the House of Savoy) (1324 - 1861)
Now pay attention, because this is about as confusing as Britain Versus the UK.
There's this former Italian state that was one of the most powerful and indeed was the one that ended up uniting the country in the Wars of Italian Independence. So why is nobody ever quite sure what its name is? Piedmont is the approximate name of the region it ruled, in the top left corner of the Italian peninsula. The word roughly means "Foot of the Mountains", which is accurate, as its habitable territory consists largely of the foothills of the Alps. Savoy is the name of the royal house which ruled Piedmont at the time and that of a nearby region which (even more confusingly) said royal family traded away to the French as part of a Batman Gambit during the wars of unification along with Nice. Therefore, the House of Savoy didn't actually rule Savoy at the time they united Italy.
Re-founded as an extension of the Holy Roman Empire, the Duchy of Savoy played a relevant role in the late Renaissance as a small but cultured realm with a love/hate relationship with France. When the French attempted to annex it, sending Duke Emmanuel Philibert into exile, he turned to Spain, which helped him recover his lands and make them militarily significant. There was even a brief project of a crusade to place his son Charles Emmanuel I at the head of a resurgent Serbian Empire against the Ottomans. Charles Emmanuel soured their relationship with Spain by provoking a war for the vacated Duchy of Montferrat, which the Spanish preferred to be inherited by the Duke of Mantua — but in a short time they were teaming up again to unsuccessfully try to prevent a Frenchman, the Duke of Nevers, from inheriting both Montferrat and Mantua. Savoy was left in a difficult position, although it would still manage to resist future French attempts of annexation.
This state is also often called the Kingdom of Sardinia, the reason for this being that the Dukes of Savoy then obtained the island because it gave them a royal dignity (the right to call themselves Kings rather than Dukes). They looked on it as very much a consolation prize (they actually wanted Sicily, and did briefly possess it before realizing that Sicily was too hard to govern from the north, so they swapped it for Sardinia). Sardinia did come in handy during The Napoleonic Wars, however, when the French conquered Piedmont (as in the bit on continental Italy) and the royal family (the aforementioned House of Savoy) fled to Sardinia, which was only part of the Kingdom of Sardinia, but now the only actual part that wasn't conquered. Confused yet?
In spite of the confusion, the most important figure to come from Piedmont (let's just call it that for these purposes) was Camillo Benso, count of Cavour. He was the mastermind of Italian Unification, although he died before the project was complete. Cavour was, in many ways, Italy's Bismarck. Although he was only the Prime Minister of Piedmont and not the King (again, like Bismarck, who was a Chancellor), he was pretty much in charge of the kingdom's affairs. Cavour took it upon himself to industrialize Piedmont, largely by exploiting Sardinia's resources, building railroads and encouraging factories, with the aid of British loans with which to build infrastructure. Once he had built Piedmont up enough to be able to project military force, he sided with the British, French, and Ottomans against Russia in the Crimean War. This had the effect of gaining an ally in the form of France's leader, Napoleon III (not to be confused with Napoleon Bonaparte, his uncle.)
With Napoleon III, Cavour was able to fight Austria and acquire most of Northern Italy (save for Venice). In return, Piedmont had to surrender Savoy and Nice to France, a bargain which still left Piedmont with far more land than it had before the war. With victories in Southern Italy, the unification of the country was nearly compete, but sadly, Cavour died after falling ill (probably with malaria). Nevertheless, Italy was united about nine years later, with Venice and Rome joining the country which Cavour (and Garibaldi) had largely built out of the various regions.
The capital of Savoy/Piedmont/Sardinia/Whatever varied between the centuries, but at the time of Italian unification was Turin.
San Marino (301 - present day)
The only Italian city-state to survive to the present day practically unchanged. It escaped the French Revolutionary and Napoleonic Wars because Napoleon admired it, considering it a model of good governance. Due to its sheltering Garibaldi during the wars of unification, the Kingdom of Italy honored its wishes to remain independent, as did Mussolini. As is traditional for Italian republics, it elects its leaders on very short terms, a matter of months. Bizarrely it was also the first place in the world to democratically elect a Communist government, and the only Western European State that got a coup by the US because of the Communist government.
The Kingdom of the Two Sicilies (1811 - 1861)
Basically Sicily and Naples, covering all of Southern Italy, the Kingdom of the Two Sicilies was by far the largest of the pre-unification states and the one with the most convoluted story, sometimes being one of the richest and sometimes being the poorest.
Their fortune was also tied to Spain, with the Spanish crown inheriting Sicily and later half-conquering-half-inheriting Naples during the Italian Wars. As part of their empire, Naples became insanely rich, its population ballooning and its capital city competing for the top 3 of the largest cities in Europe with Paris and Antwerp, but was also constantly under attack by Ottomans. Plagues and the War of the Spanish Succession finished its golden age, and although it later became an independent kingdom again, it never recovered.
By the early 19th, although Naples was still the third largest city in Europe, the kingdom itself was poor and underdeveloped and a byword for corruption and poor rule. The royal family were a branch of the Bourbons, the originally French dynasty that still reigns in Spain and Luxembourg, but aside from their first local exponent, never achieved much popularity in Italy. In 1860, the kingdom collapsed in the face of Garibaldi's invasion.
It was only officially known as the "Kingdom of the Two Sicilies" after The Napoleonic Wars, but that had been used informally as a name for many years previously.note Part of the reason why it had a poor record in war was because it had been a bargaining chip in many of the wars between the great powers and its people were indifferent towards defending their king - because he was probably a foreigner who'd been installed twenty years ago and wouldn't be any different from the one they'd be given by whoever won the war.
(You may have noticed a glaring omission from this list of major Italian cities. For the region ruled from Rome in this time period, see The Papal States.)