Indentify where strong nation-states emerged during the nineteenth century. How did the nation-state idea challenge certain polities and other organized groups?

Nationalism was the most significant political and socio-economic movement of the 19th century. Interestingly enough, it is also one of the main causes of the First World War. Among the strongest nations to emerge during this revolutionary time were France, Germany, Italy, and Russia.
In France, the French Revolution in 1789 was one of the greatest turning points in French and European history. It became obvious that democracy was going to be inevitable, and thus begun an interesting decade of various political regimes. The First French Republic was formed during the French Revolution. However, Napoleon Bonaparte crowned himself emperor in 1804, and subverted the First Republic. After his defeat at Waterloo (1815), the French monarchy had several emperors. The Second French Republic came to an end when Napoleon’s nephew, Louis Napoleon, claimed imperial power in 1852 as Napoleon III. As he wasn’t the most capable of leaders, he was blamed for leading France into war with Prussia, during which he was captured by the Prussian forces and Paris was defeated.
In Germany, Napoleon managed to dissolve the Holy Roman Empire in 1806. The most prominent figure to emerge was the chancellor Otto von Bismarck, who was a great nationalist. He unified Germany as a nation-state and fought several short lasting wars against Denmark, France and Austria, thus the formation of the new German Empire, which was one of the strongest nations of the 19th century. The conflict between the German Empire and the Austro-Hungarian Empire was a pivotal moment in German history. The political violence and the bold German ambitions in Austria and France ultimately led to the First World War.
In Italy, the most significant movement of the 19th century was the Risorgimento (revival), which began with the liberal middle classes. It was, essentially, a movement which unified the different states of the Italian peninsula into one nation-state known as the Kingdom of Italy in 1861. There were two sides: the Mezzogiorno (the South) which fought for liberalism, and the Catholic Church lead by the Pope, who greatly opposed liberalism. He mocked the Mezzogiorno, and considered them illiterate, poor people who didn’t have respect for tradition and culture, until he lost his power in 1870.
Britain and France were among the strongest nations before 1850s, but after that, they were outshone by the growing power of Russia. Russia’s main goal was to catch up with the West, which is why they concentrated on industrialization and modernization. After Tzar Alexander I died, the Minister of Finance, Sergei Witte, used foreign investment to drive the industrial revolution in the 1890s. Thus, Russia finally caught up to the West.
It is noteworthy to mention that Greece, aided by the Russian Empire, The Kingdom of France, and Great Britain, had successfully managed to gain independence from the Ottoman Empire between 1821 and 1830, a period known in history as the Greek War of Independence or the Greek Revolution.