The Roman Empire gets divided in two empires in 395: the West Roman Empire and the East Roman Empire. The West Roman Empire is defeated by germanic tribes under Odoaker in 476. In 488 Odoaker is defeated by the Ostrogoths, who form the Kingdom of the Ostrogoths. In 539 its capital Ravenna is seized by the East Roman Empire, that finishes its conquest of Italy in 555. The East Romans are defeated between 568 and 572 by the germanic tribe of the Lombards. The Kingdom of the Lombards is a fact for two centuries.

Most parts of Italy are conquered by the Frankish Realm in 774. The King of the Franks, Charlemagne, is crowned Roman Emperor in 800. Northern Italy shares the history of the East Frankish Empire (later Germany) for a long time (formally large parts remain part of the German Empire until 1806). Italy becomes an oft-changing succession of small states, principalities and kingdoms, which fought among themselves and are subject to ambitions of foreign powers. Rome becomes the centre of the Papal State and the rest of Italy gets divided in many small states. The most important Northern Italian states are Genoa, Venice and Tuscany (Florence, Pisa and Lucca). South Italy is under control of foreign powers like Aragon.

Aragón establishes in 1326 the Kingdom of Sardinia in a personal union with Aragon, later with Spain. The commercial prosperity of northern and central Italian cities, beginning in the 11th century and the influence of the Renaissance mitigate somewhat the effects of these medieval political rivalries. At the beginning of the 16th century Italy suffers the effects of an economic crisis. Most of the small and weak Italian states are defeated by foreign powers (mainly Spain); some of them (e.g. Milan and Naples) are annexed, others (e.g. Venice and Florence) are reduced to a lesser role. At the end of the 18th century, Italy is almost in the same political conditions as in the 16th century; the only differences are that Austria has replaced Spain as the dominant foreign power. The personal union between Aragón, than part of Spain, and Southern Italy ends in 1718 when the Duke of Savoye and Piedmonte (in Northern Italy) become king of Sardinia, also known as , the pre-decessor of modern Italy.

This situation deeply changed in 1796, when French armies led by Napoleon invade Italy; even if the states they create (such as the Cisalpine Republic) are essentially satellites of France, they start a nationalist movement.

These states don't not survive the fall of Napoleon and the Congress of Vienna left Italy divided between Austria (in the north-east and Lombardy), Sardinia in the northwest and in Sardinia, the Kingdom of the two Sicilies in the south and in Sicily, and the Tuscany, the Papal States and some other minor states in the centre. This situation changes rapidly between 1859 and 1861: in 1859 the liberal prime minister of Sardinia, Camillo Benso, conte di Cavour, defeats in an alliance France Austria conquering Lombardy; this leads also to the annexation of some territories in central Italy, including Tuscany. In 1860 Giuseppe Garibaldi led the a revolutionary expedition to Sicily and southern Italy, where he repeatedly defeats the Bourbon army, overthrows the king and offering his conquests to the king of Sardinia. Sardinia is restyled in 1861 in the Kingdom of Italy.

Italy incorporates Venice in 1866 and the Papal States in 1870. Italy is reunited. From 1861 until 1922, Italy is a constitutional monarchy with a parliament elected under limited suffrage (in 1913, the first universal male suffrage election was held). Although there is no real political party, the political life is dominated by liberals, divided into two factions, Destra (right) and Sinistra (left). In the 1870s and 1880s the main prime ministers are Agostini Depretis, Benedetto Cairoli and Francesco Crispi, all more or less belonging to Sinistra. In 1882 Italy signs the defensive Triple Alliance with Austria-Hungary and Germany and some years later it starts colonial expansion in the african territory of Eritrea and then of part of Somalia, but the attempt to conquer neighbouring Ethiopia failed miserably in 1896 (First Italo-Abyssinian War). This, together with social unrest in 1898 and the assassination of king Umberto I in 1900 almost leads to an authoritarian regime. Instead, the figure of the liberal Giovanni Giolitti emerges. He becomes prime ministere for the second time in 1903 and is that from 1903-1905, 1906-1909, 1911-1914 and 1920-1921. Despite widespread corruption, his governments accelerate the modernization of the country (for example, they introduced universal male suffrage). However in 1911 he bows to nationalist pressure and starts a successful war with the Ottoman empire, conquering Lybia and some islands in the Aegean Sea. In 1915 the Italian government agrees to declare war on Austria in exchange for several territories (Trento, Trieste, Istria, Dalmatia).

Under the postwar settlement, Italy receives most of the territories which were promised in the 1915 agreement, except for Dalmatia, which is given to the newly formed Yugoslavia. This generates a lot of discontent between nationalists, who started talking about "crippled victory". Furthermore, the parliament elected in 1919 is dominated by strong socialist and catholic parties, which effectively prevents the formation of a stable government, and the years 1919-1920 are called "il Biennio rosso" - the two red years - because some Italian workers, inspired by the Russian revolution begin taking over their factories, mills, farms and workplaces. In 1921 Giolitti resigns. He is succeeded by Ivanoe Bonomi (Partito Socialista Reformista Italiano (Italian Social Reform Party, PSRI) and in 1922 by the liberal Luigi Facta. The liberal establishment, for fear of a socialist revolution starts to endorse the small Partito Nazionale Fascista (National Fascist Party, PFN), led by Benito Mussolini, whose violent reaction to the strikes (by means of the "Black shirts" party militia) is often compared to the relatively moderate reactions of the government, which refrain from unnecessary violence.

In 1922 the fascists attempt a coup (the so-called "Marcia su Roma", i.e. March upon Rome). The king forms an alliance with Mussolini and convinces the liberal party to endorse a fascist-led government. Over the next few years, Mussolini (who became known as "Duce", leader) eliminates all political parties and curtails personal liberties with the pretext of the fear of a revolution. The fascists finally install an authoritarian regime. In 1929 Mussolini signed the Lateran Pacts with the catholic church, leading to the formation of the tiny independent state of Vatican City. Italy enters World War II as a ally of Germany. It annexes Albania and Ethiopia and occupies parts of neigbouring Yugoslavia. An anti-fascist popular resistance movement grows during the last 2 years of the war, harassing German forces before they were driven out in 1945. The first prime minister after the dictatorship is Ferrucio Parri of the liberal Partido d'Azione (Action Party, PdA).

After the Italian defeat in this war, Italy is restyled into the Italian Republic in 1946. A constituent assembly is elected to write a constitution for the new republic. Under the 1947 peace treaty, minor adjustments were made in Italy's frontier with France, the eastern border area was transferred to Yugoslavia, and the area around the city of Trieste was designated a free territory. Italy is now a parliamentary democratic republic dominated by the Democrazia Cristiana (Christian Democracy, DC) and the Partito Comunista Italiano (Italian Communist Party, PCI). DC is in power most of the time in coalitions wit several allies. The DC holds the government for about 45 years, despite the perennial internal struggles after the death of De Gasperi (1954). During this rule there are many prime ministers, the most important being Alcide de Gasperi (1945-1953), Amintore Fanfani (1954, 1958-1959 and 1960-1963 and far later 1982-1983 and in 1987), Antonio Segni (1955-1957 and 1959-1960). Italy is a co-founder of the European Communities in 1957 (renamed European Union in 1993). Later dominant prime ministers are Aldo Moro (1963-1968 and 1974-1976) and Giulio Andreotti (1972-1973 and 1976-1979).

After the student agitations at the end of the sixties which involves major industrial action (the so called Hot Autumn), in the seventies Italy faced a severe internal terrorism campaign. This comes mostly from the extreme left-wing movement of the Red Brigades (whose most famous act was the assassination of the former prime minister Aldo Moro in 1978), but also from extreme right-wing movements allied with uncontrolled parts of the secret services. In the eighties, for the first time, two governments were led by Giovanni Spadolini of the liberal Partito Repubblicano Italiana (Italian Republican Party, PRI) in 1982 and by Bettino Craxi of the Partito Socialista Italiano (Italian Socialist Party) from 1983 until 1987. The DC remains the main force behind the government. Craxi is succeeded by Fanfani in 1987, by Giovanni Goria (1987-1988), by Ciriaco De Mita (1988-1989), by Giulio Andreotti (1989-1992) and in 1992 by Giuliano Amato of the PSI.

At the beginning of the 90s the Italian political world is deeply shaken by a series of corruption scandals (collectively known as Mani Pulite, "Clean Hands") involving all the major parties, but especially those in the government coalition: between 1992 and 1994 the DC undergoes a severe crisis and splits up into several pieces, while many other literally melt away. The PCI splits into the Partito Democratico della Sinistra (Left Democratic Party, PDS), which was moving towards the centre of the political spectrum, and the Partito della Rifondazione Comunista (Communist Refoundation Party, PRC), which vowed to remain communist. The void on the center-right side is filled by the Alleanza Nazionale (National Alliance, AN) and by two new parties, the Lega Nord (Northern League), which runs on a semi-racist platform (sometimes advocating the formation of a separate northern Italian state), and, most importantly, by Forza Italia ("Go Italy!", FI), the populist party formed by the media tychoon Silvio Berlusconi. As a non-partisan Carlo Azeglio Ciampi becomes prime minister from 1993 until 1994. The 1994 elections sweeps Berlusconi into office as prime minister. Berlusconi, however, is forced to step down in 1995 when one member of his coalition withdraws support.