[1] During World War II, the previously independent Republic of Lithuania was occupied by the Red Army on 16 June 1940, in conformity with the terms of the 23 August 1939 Molotov–Ribbentrop Pact, and established as a puppet state on 21 July.

In these circumstances a Lithuania–USSR agreement on mutual assistance was signed in Moscow on 10 October 1939, allowing a Soviet military presence in Lithuania.

[5] A total of 18,786 Red Army troops were deployed at strategically important locations within the country: Alytus, Prienai, Gaižiūnai, and Naujoji Vilnia.

The ultimatum said Lithuania should remove officials that the USSR found unsuitable (the Minister of the Interior and the Head of the Security Department in particular), replace the government, and allow an unlimited number of Red Army troops to enter the country.

The acceptance of the ultimatum would have meant the loss of sovereignty, but Soviet foreign minister Vyacheslav Molotov declared to diplomat Juozas Urbšys that, whatever the reply may be, "troops will enter Lithuania tomorrow nonetheless".

[8] The ultimatum was a violation of every prior agreement between Lithuania and the USSR and of international law governing the relations of sovereign states.

On 17 June, the cabinet resolved that Smetona had effectively abandoned his post by leaving the country and confirmed Merkys as president without any qualifiers.

On 3 August, a Lithuanian delegation of prominent public figures was dispatched to Moscow to sign the document by which Lithuania acceded to the USSR.

The Lithuanian Activist Front (LAF), a resistance organisation founded in Berlin and led by Kazys Škirpa whose goal was to liberate Lithuania and re-establish its independence, cooperated with the Nazis.

[13] Škirpa was named prime minister in the Provisional Government of Lithuania; however, the Germans placed him under house arrest and dissolved the LAF on 5 August 1941.

The situation was so extreme that even Sniečkus complained to Lavrentiy Beria on 23 July that "If such robbery and violence continues in Kaunas, this will burst our last sympathy for the Red Army".

[17] In a special report on the situation in the Klaipėda Region, the head of the local NKGB operational group wrote that: A beautiful city, Šilutė, left by the Germans without a battle, currently looks repulsive: there is not one remaining store, almost no flats that are suitable for living.

... Metal scrap collection teams are blowing up working agricultural machinery, engines of various kinds, stealing valuable equipment from the companies.

In December 1944, Chief of the Priekulė KGB Kazakov wrote to the LSSR Minister of the Interior Josifas Bertašiūnas that due to the soldiers' violence most of the houses in Priekulė were unsuitable for living in: windows were knocked out, fireplaces disassembled, furniture and agricultural inventory broken up and exported as scrap.

[19] "On the night of 20 October, aviation unit senior M. Kapylov, by taking revenge against 14-year-old Marija Drulaitė who refused to have sexual intercourse, killed her, her mother, uncle Juozas and severely injured a 12-year-old."

Since kolkhozes had to donate a large portion of their produce to the state, the people working there lived in poorer conditions than the rest of the nation.

This process of industrialisation was followed by urbanisation, as villages for the workers had to be established or expanded in the vicinity of the new factories,[26] resulting in new towns such as Baltoji Vokė, Naujoji Akmenė, Elektrėnai and Sniečkus or expansion of old ones such as Jonava.

People were encouraged into atheism in an attempt to secularise Lithuania, with monasteries closed, religion classes prohibited and church-goers persecuted.

The second Soviet occupation was followed by armed resistance in 1944–1953, aiming to restore an independent Lithuania, re-establish capitalism and eradicate communism, and bring back national identity and freedom of faith.

Despite guerrilla warfare failing to achieve its objectives and claiming the lives of more than 20,000 fighters, it demonstrated to the world that Lithuania's joining the USSR had not been a voluntary act and highlighted the desire of many Lithuanians to be independent.

On 12 December 1947 the Central Committee of the Lithuanian Communist Party resolved that actions against supporters of resistance were too weak and that additional measures were in order.

The second major mass deportation, known as Operation Priboi, took place on 25–28 March 1949, during which the authorities put 28,981 persons into livestock cars and dispatched them deep into the USSR.

[35] The dissidents ensured that the world would receive information about the situation in the LSSR and human rights violations, which caused Moscow to soften the regime.

[39] On 23 August 1987, the Lithuanian Liberty League initiated an unsanctioned meeting in front of the monument to Adomas Mickevičius in Vilnius.

The LSSR de facto ceased to exist on 11 March 1990, with the Reconstituent Seimas declaring Lithuania's independence restored.

Therefore, Lithuania argued that all acts leading up to the Soviet takeover were ipso facto null and void, and it was simply reasserting an independence that still existed under international law.

While other republics held the union-wide referendum in March to restructure the Soviet Union in a loose form, Lithuania, along with Estonia, Latvia, Armenia, Georgia, and Moldova did not take part.

Other countries followed suit after the failed coup in August, with the State Council of the Soviet Union recognising Lithuania's independence on 6 September 1991.

[44] Overall, in the Eastern Bloc, systems without competition or market-clearing prices became costly and unsustainable, especially with the increasing complexity of world economics.

[45] Such systems, which required party-state planning at all levels, collapsed under the weight of accumulated economic inefficiencies, with various attempts at reform merely contributing to the acceleration of crisis-generating tendencies.