In October 1920, Poland annexed Vilnius, the historic and modern capital of Lithuania, and the area surrounding it; known as Żeligowski's Mutiny, this action caused ongoing tension between the two powers in the interwar period.

[7] Kazys Grinius had chaired a post-World War I repatriation commission, and served as head of the 6th cabinet of ministers and in the First and Second Seimas.

[8] Mykolas Sleževičius served as prime minister in 1918 and 1919, oversaw the organization of the Lithuanian armed forces in 1920, and was a member of the Second Seimas between 1922 and 1926.

For the first time since 1920, the bloc led by the Lithuanian Christian Democratic Party, which strongly supported the Roman Catholic Church and its clergy, did not win a majority.

The Lithuanian people were disillusioned with this party, whose members had been involved in several financial scandals: Juozas Purickis had used his diplomatic privileges in Moscow to deal in cocaine and saccharin; Eliziejus Draugelis and Petras Josiukas [lt] purchased cheap low-quality smoked pig fat from Germany instead of from Lithuanian farmers; and the minister of finance, Vytautas Petrulis, transferred a large sum of money from the state budget to his personal account.

[13] The decision implied that the Pope had recognized the Polish claims to Vilnius, creating a loss of prestige for the Christian Democrats.

But the coalition still did not constitute a majority, and went on to add representatives of minorities in Lithuania – Germans from the Klaipėda Region, Poles, and Jews.

Historians have pointed to specific European precedents in the 1920s that may have had an influence, including the 1922 March on Rome by Benito Mussolini in Italy and the May 1926 Coup of Józef Piłsudski in Poland.

[15] According to historian Anatol Lieven, Smetona and Voldemaras saw themselves as the dispossessed true heroes of the independence movement, who despaired of returning to power by democratic means.

[16] After the May elections, the Grinius/Sleževičius government lifted martial law, still in effect in Kaunas and elsewhere, restored democratic freedoms, and granted broad amnesty to political prisoners.

Many released prisoners were communists who quickly used the new freedoms of speech to organize a protest attended by approximately 400 people in Kaunas on 13 June,[11] a day after the acquittal of 92 members of the Workers' Group of Lithuania.

[12] Another public outcry arose when the government, seeking the support of ethnic minorities, allowed the opening of over 80 Polish schools in Lithuania.

[13] The coalition government directly confronted the Christian Democrats when it proposed a 1927 budget that reduced salaries to the clergy and subsidies to Catholic schools.

[19] On 20 September 1926, five military officers led by Captain Antanas Mačiuika [lt] organized a committee which included generals Vladas Nagevičius and Jonas Bulota among its members.

Colonel Kazys Škirpa, who had initiated the military reform program,[13] tried to rally troops against the coup, but was soon overpowered and arrested.

The military strove to create the impression that the coup had been solely their initiative, that Smetona had not been involved at all, and he had joined only in response to an invitation to become the "savior of the nation".

Smetona and Voldemaras, both representing the Lithuanian National Union, invited the Christian Democrats to join them in forming a new government that would restore some degree of constitutional legitimacy.

Looking toward the near future, the Christian Democrats reasoned that they could easily win any upcoming Seimas elections and regain power by constitutional means and avoid direct association with the coup.

Initially, President Grinius refused to resign, but he was eventually persuaded that a Polish invasion was imminent and Smetona had sworn to uphold the constitution.

About 350 communists were arrested, and four leaders (Karolis Požela, Juozas Greifenbergeris, Kazys Giedrys and Rapolas Čarnas) were executed on 27 December.

[13] However, other sources cite Captain Vincas Jonuška, allegedly shot by the guards of the Presidential Palace, who died a day later in a hospital.

[22] Christian Democrats, believing that the coup was merely a temporary measure, demanded that new elections to the Seimas be held, but Smetona stalled.

[13] In April, a group in the Lithuanian Popular Peasants' Union tried to organize a coup "to defend the constitution," but the plans were discovered and the rebels were arrested.

[24] As a result, the Lithuanian National Union took the upper hand in its dispute with a much larger and influential rival and assumed absolute control of the state.

[5] The coup continued to be a difficult issue for Lithuanians, since the Soviet Union went go on to describe its subsequent occupation of Lithuania as a liberation from fascism.

Encyclopædia Britannica, however, describes the regime as authoritarian and nationalistic rather than fascist,[25] a view not shared by historian Mindaugas Tamošaitis, who wrote in the Visuotinė lietuvių enciklopedija that "In the late 1930s, the younger generation that assuming leadership of the party proclaimed radical right-wing attitudes [such as] sympathy for Italian fascism, etc".

[26] The coup's apologists have described it as a corrective to an extreme form of parliamentarianism, justifiable in light of Lithuania's political immaturity.