thumb|300px|Map of the plebiscite areas<br />Pink = Germany<br />Green = Poland<br />Lilac = Czechoslovakia (including, without plebiscite, [[Hlučín Region|Hlučín)<br />Pale green = to Poland following plebiscite<br />Orange = remaining in Germany following plebiscite]]

The Upper Silesia plebiscite was a plebiscite mandated by the Versailles Treaty and carried out on 20 March 1921 to determine ownership of the province of Upper Silesia between Weimar Germany and the Second Polish Republic. The region was ethnically mixed with both Germans and Poles. According to prewar statistics, ethnic Poles formed 60 percent of the population.

Under the previous rule by the German Empire, Poles claimed they had faced discrimination and had been effectively second-class citizens. The period of the plebiscite campaign and the Allied occupation was marked by violence. Three Polish uprisings occurred, and German volunteer paramilitary units came to the region.

The area was policed by French, British and Italian troops and overseen by an Interallied Commission. The Allies planned a partition of the region, but a Polish insurgency took control of over half the area. The Germans responded with the Freikorps, volunteer paramilitary units from all over Germany that fought the Polish units. The Freikorps from all over Germany participated in the plebiscite, as well as other bussed-in Germans. In the end, after renewed Allied military intervention, the final position of the opposing forces became, roughly, the new border. The decision was handed over to the League of Nations, which confirmed the border, and Poland received roughly one third of the plebiscite zone by area, including the greater part of the industrial region.

After the referendum, a conference of ambassadors in Paris on 20 October 1921 decided to divide the region. Consequently, the German-Polish Accord on East Silesia (Geneva Convention), a minority treaty, was concluded on 15 May 1922 and dealt with the constitutional and legal future of Upper Silesia, which had partly become Polish territory.

Ethnolinguistic structure before the plebiscite

thumb|Language situation in Silesia in 1905-06

The earliest exact census figures on ethnolinguistic or national structure (Nationalverschiedenheit) of the Prussian part of Upper Silesia, come from 1819. Polish immigration from Galicia, Congress Poland and Prussian provinces into Upper Silesia during the 19th century was a major factor in their increasing numbers. The last Prussian general census figures available are from 1910 (if not including the 1911 census of school children – Sprachzählung unter den Schulkindern – which revealed a higher percent of Polish-speakers among school children than the 1910 census among the general populace). Figures (Table 1.) show that large demographic changes took place between 1819 and 1910, with the region's total population quadrupling, the percent of Germans increasing significantly, while Polish-speakers maintained their steady increasing numbers. Also the total land area in which Polish was spoken, as well as the land area in which it was spoken, declined between 1790 and 1890. Polish authors before 1918 estimated the number of Poles in Prussian Upper Silesia as slightly higher than according to official German censuses.

The three western districts of Falkenberg (Niemodlin), Grottkau (Grodków) and Neisse (Nysa), though part of Regierungsbezirk Oppeln, were not included in the plebiscite area, as they were almost entirely populated by Germans.

{| class="wikitable"

! colspan="18" | Table 1. Numbers of Polish, German and other inhabitants (Regierungsbezirk Oppeln)

|-

!Year

!1819

!1828

!1831

!1834

!1837

!1840

!1843

!1846

!1852

!1855

!1858

!1861

!1867

!1890

!1900

!1905

!1910

|-

| Polish

|377,100

(67.2%)

| 418,837

(61.1%)

| 443,084

(62.0%)

|468,691

(62.6%)

| 495,362

(62.1%)

| 525,395

(58.6%)

| 540,402

(58.1%)

| 568,582

(58.1%)

| 584,293

(58.6%)

|590,248

(58.7%)

| 612,849

(57.3%)

| 665,865

(59.1%)

| 742,153

(59.8%)

| 918,728 (58.2%)

| 1,048,230 (56.1%)

| 1,158,805 (57.0%)

| Census, monolingual Polish: 1,169,340 (53.0%)

or up to 1,560,000 together with bilinguals

A feature of the plebiscite campaign was the growing prominence of a strong autonomist movement, the most visible branch of which was the Bund der Oberschlesier/Związek Górnoślązaków, an organisation attempted to gain promises of autonomy from both states and possible future independence for Upper Silesia.

There were 1,186,758 votes cast in an area inhabited by 2,073,663 people. They resulted in 717,122 votes being cast for Germany and 483,514 for Poland.

The towns and most of the villages in the plebiscite territory had German majorities. However, the districts of Pless (Pszczyna) and Rybnik in the southeast, as well as Tarnowitz (Tarnowskie Góry) in the east and Tost-Gleiwitz (Gliwice) in the interior showed considerable Polish majorities, while in Lublinitz (Lubliniec) and Groß Strehlitz (Strzelce Opolskie) the votes cast on either side were practically equal. All districts of the industrial zone in a narrower sense – Beuthen (Bytom), Hindenburg (Zabrze), Kattowitz (Katowice), and Königshütte (Chorzów) – had slight German majorities, but in Beuthen and Kattowitz, that was entirely because of the town vote (four fifths in Kattowitz. compared to an overall 60%). Many country communes of Upper Silesia had Polish majorities. Overall, however, the Germans won the vote by a measure of 59.4% to 40.6%. The Interallied Commission deliberated, but the British proposed a more easterly border than the French, which would have given much less of the Industrial Triangle to Poland.

thumb|A crowd awaits the plebiscite results in Oppeln (Opole)

thumb|1920 special passport issued to those living in the region during the Upper Silesian plebiscite.

In late April 1921, when pro-Polish forces began to fear that the region would be partitioned according to the British plan, elements on the Polish side announced a popular uprising. Korfanty was the leading figure of the uprising, but he had much support in Upper Silesia and from the Polish government, in Warsaw. Korfanty called for a popular armed uprising, whose aim was to maximize the territory that Poland would receive in the partition. German volunteers rushed to meet this uprising, and large-scale fighting took place in the late spring and early summer of 1921. German-speaking spokesmen and German officials complained that the French units of the Upper Silesian army of occupation supported the insurrection by refusing to put down violent activities or to restore order.

Twelve days after the start of the uprising, Korfanty offered to take his Upper Silesian forces behind a line of demarcation if the released territory was occupied not by German forces but by Allied troops. On 1 July, British troops returned to Upper Silesia to help French forces occupy this area. Simultaneously with those events, the Interallied Commission pronounced a general amnesty for the illegal actions committed during the recent violence except for acts of revenge and cruelty. The German defence force was finally withdrawn.

Because the Allied Supreme Council was unable to come to an agreement on the partition of the Upper Silesian territory on the basis of the confusing plebiscite results, a solution was found by turning the question over to the Council of the League of Nations. Agreements between the Germans and Poles in Upper Silesia and appeals issued by both sides, as well as the dispatch of six battalions of Allied troops and the disbandment of the local guards, contributed markedly to the pacification of the district. On the basis of the reports of a League commission and those of its experts, the Council awarded the greater part of the Upper Silesian industrial district to Poland, which obtained almost exactly half of the 1,950,000 inhabitants (965,000) but not quite a third of the territory (only 3,214.26&nbsp;km<sup>2</sup> (1,255&nbsp;mi<sup>2</sup>) out of 10,950.89&nbsp;km<sup>2</sup> (4,265&nbsp;mi<sup>2</sup>)) but more than 80% of the heavy industry of the region.

The German and Polish governments, under a League of Nations recommendation, agreed to enforce protections of minority interests that would last for 15 years. Special measures were threatened in case either state refused to participate in the drawing up of such regulations or to accept them subsequently. In the event, the German minority remaining on the Polish side of the border suffered considerable discrimination in the subsequent decades.

The Polish government, convinced by the economic and political power of the region and by the autonomist movement of the plebiscite campaign, decided to give Upper Silesia considerable autonomy, with a Silesian Parliament as a legislature and the Silesian Voivodship Council as the executive body. On the German side the new Prussian province of Upper Silesia (Oberschlesien) with regional government in Oppeln was formed, likewise with special autonomy.

Results

thumb|Map of Upper Silesian Plebiscite of 1921|center|1024x1024px

{| class="wikitable sortable"

|- style="width:80px"

! County

! population (1919)

! registered voters

! turnout

! votes for Germany

!%

! votes for Poland

!%

|-

|Beuthen (Bytom), town

||71,187

||42,990

||39,991

||29,890

|| 74.7%

||10,101

|| 25.3%

|-

|Beuthen (Bytom), district

||79,973

||51,364

||50,100

||37,651

|| 75.2%

||12,449

|| 24.8%

|-

|Gleiwitz (Gliwice), town || 69,028

||41,949

||40,587

||32,029

|| 78.9%

||8,558

|| 21.1%

|-

|Groß Strehlitz (Strzelce Opolskie), district ||76,502

||46,528

||45,461

||22,415

|| 49.3%

||23,046

|| 50.7%

|-

|Hindenburg (Zabrze), district ||167,632

||90,793

||88,480

||45,219

|| 51.1%

||43,261

|| 48.9%

|-

|Kattowitz (Katowice), town ||45,422

||28,531

||26,674

||22,774

|| 85.4%

||3,900

|| 14.6%

|-

|Kattowitz (Katowice), district ||74,811

||44,052

||42,628

||31,864

|| 74.7%

||10,764

|| 25.3%

|-

|Kreuzburg (Kluczbork), district || 52,558

||40,602

||39,627

||37,975

|| 95.8%

||1,652

|| 4.2%

|-

|Leobschütz (Głubczyce), district ||78,247

||66,697

||65,387

||65,128

|| 99.6%

||259

||0.4%

|-

| Lublinitz (Lubliniec), district || 55,380

||29,991

||29,132

||15,453

|| 53.0%

||13,679

|| 47.0%

|-

|Namslau (Namysłów), district ||5,659

||5,606

||5,481

||5,348

|| 97.6%

||133

|| 2.4%

|-

|Neustadt (Prudnik), district ||51,287

||36,941

||36,093

||31,825

|| 88.2%

||4,268

|| 11.8%

|-

|Oppeln (Opole), town ||35,483

||22,930

||21,914

||20,816

|| 95.0%

||1,098

|| 5.0%

|-

|Oppeln (Opole), district ||141,828

||73,923

||72,053

||18,675

|| 25.9%

||53,378

|| 74.1%

|-

|Ratibor (Racibórz), town ||36,994

||25,336

||24,518

||22,291

|| 90.9%

||2,227

|| 9.1%

|-

|Ratibor (Racibórz), district ||54,962

||35,976

||35,007

||23,857

|| 68.1%

||11,150

|| 31.9%

|-

|Rybnik, district ||160,836

||82,350

||80,266

||27,919

|| 34.8%

||52,347

|| 65.2%

|-

|Tarnowitz (Tarnowskie Góry), district ||86,563

||45,561

||44,591

||17,078

|| 38.3%

||27,513

|| 61.7%

|-

|Tost-Gleiwitz (Gliwice), district

||2,073,663

||1,220,979

||1,186,758

||707,393

|| 59.6%

||479,365

|| 40.4%

|-

|Total without Namslau district

According to Robert Machray, a British international observer, 192,408 of all plebiscite voters were migrants and made up 16% of the total electorate. Among them, 94.7% voted for Germany. There were cases of votes being cast in the name of already deceased persons who died outside of Upper Silesia, and since their deaths were registered "in comparatively inaccessible German registration departments in Central Germany", it was often difficult to detect voter fraud. Machray establishes that many Poles were either prevented from voting or intimidated into voting for Germany and notes that in provinces such as Kozle and Olesno, a minority of voters voted for Poland although the areas were overwhelmingly Polish according to the 1910 census, with 75% in Kozle and 81% in Olesno Provinces. Machray concludes that given the aggressive anti-Polish campaign conducted by local authorities and German volunteers, "the results were far from being an objective reflection of the true desires of the oppressed people".

Comparison of district demographics with voting behaviour

The following table compares the percentage of German-speakers (excluding bilinguals) as reported in the 1910 census in each district, with the pro-German vote share registered in the respective district. In almost all districts, the percentage of pro-German votes exceeded the percentage of those who identified as German by almost 25% on average, which suggests that many non-Germans voted in favour of Germany.

{| class="wikitable sortable"

!District

!% of German Population

!100%

!3,017,981

!Divided between:

!

|-

|to Poland

|526&nbsp;km<sup>2</sup>

|2%

|1%

|Poznań Voivodeship

(Niederschlesiens Ostmark)

|

|-

|to Czechoslovakia

|325&nbsp;km<sup>2</sup>