The Chios Massacre took place in 1822 when troops from the Ottoman Empire massacred much of the civilian population of the Greek island of Chios during the Greek War of Independence. The territory that comprises modern-day Greece had been under Ottoman control for several centuries when Greek nationalism flared up in the nineteenth century. By the 1820s, this nationalism manifested itself in open revolt. The revolution was initially quelled by the Ottoman Empire, but the violent means that the Ottoman Empire employed enflamed the Greek people and was widely condemned by the international community. The major powers of Western Europe soon intervened, and in 1832, the Greek nation declared independence.

The German policy of Kulturkampf was undertaken during the reign of Otto von Bismarck in the 1870s. Its primary purpose was to dramatically weaken the influence of the Catholic Church in Germany and to secularize German society. At the time, roughly two-thirds of Germany was Protestant, but a powerful minority, particularly in formally Polish territory, still followed Catholicism. Bismarck’s primary goal was to strengthen the German government and unify German national identity at the expense of the Catholic faith.

Before 1848, the Kingdom of Hungary had long been a territory of the Holy Roman Empire, and then later the Austrian Empire, but was nominally governed independently of both. Following the failed Hungarian rebellion of 1848, the Kingdom of Hungary was suppressed by the Austrian Empire, but nationalist desires were difficult to eradicate. Following the defeat of Austria at the hands of Prussia in the Austro-Prussian War, the Austrian Empire lost much of its influence in Europe and in a desperate attempt to redefine itself in the wake of rising nationalism agreed to the Compromise of 1867, which created a dual monarchy in Austria-Hungary.

The term “Westphalian sovereignty” refers to the idea that each independent state has sovereignty and control over all the territory within its border, exclusive of any external powers. This idea underpins the nature of modern statehood and first emerged, or rather was first codified, in the Peace of Westphalia, which ended the devastating Thirty Years’ War. Due to European expansion around the world in the centuries following, the Peace of Westphalia's “Westphalian sovereignty” is generally universal in its application.

The term “irredentism” is used to describe the belief that a territory within another country’s borders should actually be part of a nation that exists either outside of or independent of those borders. Generally, in European history, it refers to a territory that was once part of a nation, such as France with Alsace-Lorraine or Germany with Austria, that has been lost in conflict and which the losing nation desires to reclaim. It is one of the more dangerous and prominent forms of European nationalism because it so often leads to war in European history.

At the height of its reach, the Austro-Hungarian Empire occupied much of Central Europe and extended south into the Balkans and East into Eastern Europe. It was composed of several distinct ethnic groups, all of whom had a shared history, language, and cultural identity. This had long been the composition of the empire, but with rising nationalism in the nineteenth century, this became a problem that was more difficult to manage. All of these ethnic groups expressed nationalist ambitions in the nineteenth century except for the Poles, who lived outside of the Austro-Hungarian Empire and were at the time primarily controlled by Russia and Germany. Each of these ethnic groups currently has its own nation-state, with all of them being self-explanatory except perhaps the Magyars (Hungary).

The Act of Union of 1801 dissolved the Irish Parliament and formally ended any semblance of Irish independence. The territory of Ireland was incorporated into the United Kingdom, now called the United Kingdom of Great Britain and Ireland. The Act of Union may be understood as a British government reaction to the Irish Rebellion of 1798 and also a response to the French Revolution a decade earlier, both of which inflamed Irish nationalism.

The Kingdom of Piedmont-Sardinia was one of the most influential and economically prosperous by the time the movement towards Italian unification began in the mid-nineteenth century. Led by Victor Emmanuel and Camillo di Cavour, the Kingdom was the primary driving force behind Italian unification. In 1861, the Kingdom of Sardinia annexed all the other territories that comprise modern-day Italy into the Kingdom of Italy.

"Irredentism" comes from the Italian phrase "Italia irredenta," which means "unredeemed Italy" and referred to those culturally and linguistically Italian regions ruled by Austria that Italian nationalists wanted to be part of a Unified Italy. Irredentism was also a key component in German unification, French nationalism, and pan-Slavic movements. Remarkably for the period, irredentism also had few ties to particular forms of government, since it was tied to ethnic, cultural, and linguistic affinities.

Garibaldi was one of the most famous revolutionaries of the mid-nineteenth century. His revolutionary career began in South America as an agitator and soldier in favor of various republican causes. He returned to Europe in the midst of the revolutions of 1848. He raised an army of volunteers to fight the Austrian Empire in order to free Northern Italy so that the entire Italian peninsula could be unified. Garibaldi was one of the central figures of the Italian Risorgimento, which resulted in the creation of the Kingdom of Italy in 1861.