In 1882, the first slet was held. Slet came from the Czech word for "a flocking of birds" (Czech plural: slety). The same word exists or can be synthesized from common Slavic roots in other Slavic languages. It meant a mass gymnastics festival that became a grand tradition within the Sokol movement that spread across Central Europe together with other Slavic movements such as the political movement of Pan-Slavism. The first and subsequent slets included an elaborate welcoming ceremony at the train station, mass demonstrations, gymnastics competitions, speeches, and theatrical events, open to members of all Sokols.
In 1887 the Habsburg authorities finally allowed, after over twenty years worth of proposals, the formation of a union of Sokol clubs – Czech Sokol Community (Česká obec sokolská, ČOS). The union centralized all the Sokols in the Czech lands and sent Sokol trainers to the rest of the Slavic world to found Sokol institutions in Kraków, Ljubljana, Zagreb, and even the Russian Empire (mostly the Ukrainian lands). In 1889, though officially forbidden by the authorities, members of the Prague Sokol went to the World's Fair in Paris. There they won several medals and established strong connections with French gymnasts and the French public. The Sokols have been credited with establishing the beginning of the strong French sympathy for the Czechs and their subsequent political alliances on this trip.
The 1890s were a progressive era for the Sokols. In order to encourage a wider range of participation, the Sokols reformed their programs, offering training sessions of varying intensities, extending their libraries, emphasizing the educational aspect of training, and starting programs for adolescents, youth, and women. There was an increasing focus on mass-based ideology and working class egalitarianism under the leadership of the Young Czechs, namely Jan Podlipný, who was also the mayor of Prague 1897–1900. The second slet was held in 1891 (over 5,000 Sokols) and the third one soon afterwards in 1895. At this third slet the congress of the Sokol union laid out its progressive new trajectory in the St. Wenceslas Day (September 28) Resolutions. The leaders chose to continue to provide more accessible forms of training, with less focus on competition and more on an egalitarian idea of people's gymnastics balancing mental as well as physical education.
The rise of the Social Democrats and agrarian parties in the political arena played out in Sokol politics as well as national ones. The Social Democrats formed a rival gymnastics society, the Workers' Gymnastics Club, (Dělnická tělovýchovná jednota, DTJ). Most Sokol leaders aligned with the Czech National Socialists after the decline of the Young Czech party, and attacked the Social Democrats as “Germans” and “Jews” opposed to the true Czech cause. Václav Kukař, a powerful ČOS figure, developed the policy of "cleansing" (očištění) and sought to limit membership to those who he believed demonstrated commitment to purely Czech causes. Most of the progressive members of the Sokols were purged or left voluntarily to join the DTJ. Another rival gymnast society was founded by the Christian-Socialist party under the name Orel ("Eagle"). In the face of such competition, the Sokols set about reaffirming their traditional mission under the leadership of Josef Scheiner. The fourth slet, held in 1901 (11,000 Sokols), boasted a large international participation, including Galician Poles, Ukrainians, Slovenes, Croats, Russians, Bulgarians, Serbs, as well as Frenchmen and Americans. This slet also marked the first appearance of women who grew to be a major part of Sokol members in the following decades.
At the 1910 meeting of the ČOS congress the sokols reaffirmed their intentions to remain "above politics" and loosened their strict membership rules to allow Social Democrats, though still not clericals, into the sokols. In 1912, the first "All-Slavic Slet" (Všeslovanský slet, over 30,000 Sokols) was held with a largely military atmosphere, causing Augustin Očenášek (a member of Sokol) to remark, "When the thunder comes and the nations rise up to defend their existence, let it be the Sokol clubs from which the cry to battle will sound". The cry to battle did sound two years later, when the first rumors of Franz Ferdinand's assassination reached the Sokol members, most of whom were attending a regional slet in Brno.
With the onset of World War I, in 1915 the Sokols were officially disbanded. Many members were active in persuading the Czechs to defect from the Austro-Hungarian army to the Russian side. Sokol members also helped create the Czechoslovak Legions and local patrols that kept order after the disintegration of Habsburg authority, and during the creation of Czechoslovakia in October 1918. They also fulfilled their title as the "Czech national army", helping to defend Slovakia against the invasion of Béla Kun and the Hungarians. The Sokol flourished in the early interwar period, and by 1930 had 630,000 members. The Sokols held one last slet (350,000 Sokols) on the eve of the Munich Agreement of 1938 and were later brutally suppressed and banned during the Nazi occupation of Bohemia and Moravia.
Members of Sokol who emigrated from Czechoslovakia set up small Sokol groups abroad. This Sokol migration, for a variety of reasons, began even before Czechoslovakia became a nation in 1918, intensified as a result of the World Wars and the Communist suppression, and continues to this day. Bohemian, Moravian, and Slovak immigrants and Czech-American citizens started the American Sokol Organization in St. Louis Missouri in 1865, only three years after the first Prague Sokol. Units quickly formed and by 1878, the United States had 13 Sokol chapters. By 1937, American Sokol membership rolls counted nearly 20,000 adults in areas as far-flung as New York City, New Jersey, Pittsburgh, Chicago, Detroit, Cleveland, Oakland, Iowa, Minnesota, Nebraska, Oklahoma, St. Louis, Texas, Nyack and parts of Canada. Senator Roman Hruska of Nebraska, who was of Czech heritage, was a lifelong member of Sokol Omaha.
After World War II Sokols held one more slet in 1948 before they were once again suppressed, this time by the Communists. The Communist Party tried to replace the tradition of slets with mass exercises employed for propaganda purposes: Spartakiad (spartakiády). The Sokols reappeared briefly during the Prague Spring of 1968. After years of hibernation, the Sokol movement was revived for the fourth time in 1990. A slet was held in 1994 (with 23,000 Sokols participating), after the fall of Communism.