(Subsequently, in April 1943, Soviet leader Joseph Stalin broke off Soviet-Polish diplomatic relations after Sikorski asked the International Red Cross to investigate the Katyn massacres.

[1] His grandfather, Tomasz Kopaszyna Sikorski, had fought and been wounded at the Battle of Olszynka Grochowska in the November Uprising, during which he received the Virtuti Militari medal.

[1][3][4] During his studies at the Polytechnic, Sikorski became involved in the People's School Association (Towarzystwo Szkoły Ludowej), an organization dedicated to spreading literacy among the rural populace.

[3] In 1908, in Lwów, Sikorski—together with Józef Piłsudski, Marian Kukiel, Walery Sławek, Kazimierz Sosnkowski, Witold Jodko-Narkiewicz [pl] and Henryk Minkiewicz—organized the secret Union for Active Struggle (Związek Walki Czynnej), with the aim of bringing about an uprising against the Russian Empire, one of Poland's three partitioners.

[3] In the first few weeks of the war he became the chief of the Military Department in the Supreme National Committee (Naczelny Komitet Narodowy, NKN) and remained in this post until 1916.

[3][4] The Legions—the army created by Józef Piłsudski to liberate Poland from Russian and, ultimately, Austro-Hungarian and German rule—initially fought in alliance with Austria-Hungary against Russia.

[4] In 1918 the Russian, Austro-Hungarian and German empires collapsed, and Poland once again became independent, but the borders of the Second Polish Republic were not fully determined and were unstable.

[10] His forces took Mozyr and Kalenkowicze in March 1920, and he would command the Polesie Group during Poland's Kiev offensive in April 1920, advancing to the Dnieper River and the Chernobyl region.

[10] As the Polish–Soviet War grew in intensity, in late April 1920 the Red Army of Russia's new Soviet regime pushed back Polish forces and invaded Poland.

[10] On 6 August he was named the commander of the newly formed Polish 5th Army, which was tasked with holding the front to the north of Modlin, between Narew and Wkra rivers.

During that battle (sometimes referred to as "the Miracle at the Vistula") Sikorski stopped the Bolshevik advance north of Warsaw and gave Piłsudski, the Polish commander-in-chief, the time he needed for his counter-offensive; beginning with the 15 August his forces successfully engaged the Soviet 5th and 15th Armies.

Based on his analysis, the Polish Council of Ministers adopted new foreign policy that would remain roughly unchanged until the late 1930s (preserving the status quo in Europe, and treating Germany and Russia as equal potential threats).

[11] His proposal to increase the powers of the minister of military affairs while reducing those of the Chief Inspector of the Armed Forces met with sharp disapproval from Piłsudski, who at that time was gathering many opponents of the current government.

[11] A democrat and supporter of the Sejm, Sikorski declared his opposition to Józef Piłsudski's May 1926 coup d'état;[11] he remained in Lwów, refused to dispatch his forces, and played no substantive role in the short struggle.

[12] Sikorski largely withdrew from active politics, spending much of his time in Paris, France, working with the French Ecole Superieure de Guerre (war college).

[12] In February the following year, together with several prominent Polish politicians (Wincenty Witos, Ignacy Paderewski, and General Józef Haller) he joined the Front Morges, an anti-Sanation] political grouping.

[12][13] On 7 November he became commander in chief and General Inspector of the Armed Forces (Naczelny Wódz i Generalny Inspektor Sił Zbrojnych), following Rydz-Śmigły's resignation.

[21] That concept, although ultimately futile, gained some traction around that time, as Sikorski and Edvard Beneš from the Czechoslovak government-in-exile, signed an agreement declaring the intent to pursue closer cooperation on 10 November that year.

[4] The Polish Government reached an agreement with the Soviet Union (the Sikorski-Maisky Pact of 17 August 1941), confirmed by Joseph Stalin in December of that year.

Stalin agreed to invalidate the September 1939 Soviet-German partition of Poland, declare the Russo-German Molotov–Ribbentrop Pact of August 1939 null and void, and release tens of thousands of Polish prisoners-of-war held in Soviet camps.

[4] Stalin claimed that the atrocity had been carried out by the Germans,[24] while Nazi propaganda orchestrated by Joseph Goebbels successfully exploited the Katyn massacre to drive a wedge between Poland, the Western Allies and the Soviet Union.

[5] On 4 July 1943, while Sikorski was returning from an inspection of Polish forces in the Middle East, he was killed, together with his daughter, his chief of staff Tadeusz Klimecki, and seven others, when his plane, a Liberator II, serial AL523, crashed into the sea 16 seconds after takeoff from Gibraltar Airport at 23:07 hours.

[29] On 14 September 1993, his remains were exhumed and transferred via Polish Air Force TU-154M, and escorted by RAF 56 Sqn Tornado F3 jets, to the royal crypts at Wawel Castle in Kraków, Poland.

[31][32] Only four months after Sikorski's death, in November 1943, at Tehran, Churchill and Roosevelt agreed with Stalin that the whole of Poland east of the Curzon Line would be ceded to the Soviets.

"[33] After the Teheran Conference, Stalin decided to create his own puppet government for Poland, and a Committee of National Liberation (the PKWN) was proclaimed in the summer of 1944.

"[34] Mikołajczyk would serve as prime minister's until 24 November 1944 when, realizing the increasing powerlessness of the Polish Government-in-Exile, he resigned and was succeeded by Tomasz Arciszewski, "whose obscurity", according to historian Mieczysław B. Biskupski, "signaled the arrival of the government in exile at total inconsequentiality.

[36] By the time of the Potsdam conference in 1945, Poland had been relegated to the Soviet sphere of influence – an abandonment of the Polish Government-in-Exile that led to the rise of the Western-betrayal concept.

[5] In its aftermath, in the People's Republic of Poland, Sikorski's historic role, like that of all the adherents of the London government, would be minimized and distorted by propaganda, and those loyal to the government-in-exile would be liable to imprisonment and even execution.

In time, restrictions on discussing Sikorski began to ease; on a centennial anniversary of his birth in 1981, commemorative events were held on the Rzeszów Voivodeship, including an academic conference, and revealing of plaques in Nisko and Leżajsk.

[5] In 1981, a commemorative plaque was revealed at Hotel Rubens in London,[5] where during the war Polish Military Headquarters, including Sikorski's office, were located.