Short answers, pulled from the story.
The maritime republics were Italian coastal city-states that gained political autonomy and economic power through maritime trade, beginning in the Middle Ages. The four most recognized are Amalfi, Genoa, Pisa, and Venice, whose coats of arms have appeared on the Italian Navy flag since 1947. A longer list includes Ancona, Gaeta, Noli, and Ragusa in Dalmatia.
Swiss historian Jean Charles Leonard de Sismondi coined the expression in his 1807 work History of the Italian Republics of the Middle Centuries. None of the city-states ever called themselves maritime republics; the term was applied retrospectively by 19th-century historiography.
Their rise followed the 9th-century economic recovery in Europe, which opened Mediterranean coastal trade routes at a time when overland routes were hazardous. Cities like Amalfi, Venice, and Genoa were geographically isolated from inland armies by mountains or lagoons, allowing them to focus on the sea. They organized their own defense against Saracen pirates and gradually won administrative and then political independence from the Byzantine Empire, the Holy Roman Empire, or the Papal States.
They imported from the East goods unobtainable in Europe, including spices such as black pepper, cloves, nutmeg, and cinnamon; medicines like ginger and camphor; textiles including silk, brocade, and damask; dyes such as indigo and alum; and luxury goods including gemstones, ivory, and porcelain. These were resold across Italy and into central and northern Europe, forming a commercial triangle between the Arab East, the Byzantine Empire, and Italy.
The rivalry ended with the War of Chioggia in the late 14th century. After besieging Venice itself, Genoa was trapped and forced to surrender at Chioggia. The 1381 Treaty of Turin left Genoa militarily defeated, though it kept Cyprus. Venice, the exhausted victor, had to cede Dalmatia to Hungary but recovered in the 15th century, while Genoa's naval power went into long decline.
Venice, Genoa, and Noli all ended in 1797 during Napoleon's Italian campaign. Venice was taken directly by Napoleon and reduced to a city-state dependent on the Habsburgs. Genoa became the Ligurian Republic in 1797 and was annexed to France in 1805. Ragusa survived Venice but was assigned to France by the Peace of Pressburg in 1805 and occupied by French troops in 1806.