Author: Not Decided
Status: In Research
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I’m back and ready for action. Sorry, it took so long. Time to do some researching 
Ok, in my research here I’m trying to cover a rather controversial topic of the annexation of Zaolzie (Olsa-Gebiet) by the Polish state. I hope it will help.
When it comes to political (and overall) background of the Annexation of Bohemia I already covered it (partially) in the research I posted in the thread about The Molotov-Ribbentrop pact.
I. The background of the Annexation of Zaolzie
The term “Zaolzie” was created during the Interwar period and was referring to the western part of the former Duchy of Cieszyn inhabited mostly by Poles (Cieszyn Silesia/Teschener Schlesien). The name itself can be literally translated as “Behind Olsa”, Olsa being the river that floats in the area.
According to an Austro-Hungarian census, most inhabitants of the Cieszyn Silesia were Polish. The exact numbers are:
In the summer of 1920, during the Tuchaczewski’s offensive against Warsaw, the Czech Foreign Minister Edvard Beneš took advantage of the situation of Poland and during the conference of Spa, he managed to push the idea that the division of Cieszyn Silesia should be decided by the great powers without holding a plebiscite. Polish prime minister Władysław Grabski agreed on this idea counting on the help of the great powers in the face of the Bolshevik invasion of Poland.
As a result of Czech propaganda and the ties of Beneš and President Tomáš Masaryk to the western elites, the powers decided to give Cieszyn Silesia on July 28, 1920, to Czechoslovakia. The Czechs obtained the Polish land that was granted to them after the war of 1919, the entire demilitarized zone and some of the remains of the Polish territory given to Poland after the war of 1919, including the towns of Třinec, Karvina, Jabłonki and the southern districts of Cieszyn. On top of that Czechoslovakia received most of the contested areas of Spiš and Orava.
The Polish government recognized the decision of the Council of Ambassadors due to the deteriorating situation at the front of the Polish-Bolshevik war, under a condition that Czechoslovakia will allow transport of weapons for the Polish Army through the Czechoslovakian territory. Despite the declarations of Edvard until the Battle of Warsaw, Czechoslovakia did not let any transports to Poland.
Polish newspaper “Robotnik Sląski” (“Silesian Worker”) informing about the decision of the Council of Ambassadors. The headline says: “We were sold to the Czechs!”
II.The Annexation of Zaolzie
After the end of the Munich conference on September 30, 1938, and the Czechoslovak government’s recognition of territorial assignments for Germany, guaranteed by France, Germany, Great Britain, and Italy, Poland demanded on September 30, 1938, at 11.45 p.m. from the Czechoslovak government to correct the Polish-Czechoslovak border in Zaolzie. The territory was to be divided alongside the ethnic borders. The Czechoslovak government agreed to the Polish demands.
On October 2, 1938, 35 thousand troops of the Polish Army under command of Władysław Bortnowski entered Zaolzie welcomed by the Polish community. It is important to point out that actions undertaken by Poles were in fact not consulted in any way with the Germans. There was no cooperation. Which lead to a sort of a race between the Polish and German forces to take their objectives before the other. It, of course, led to a couple of incidents like in Bogumin.
Polish newspaper “Ilustrowany Kuryer Codzienny” showing photos of Polish 7TP tanks during the Annexation of Zaolzie.
Sources:
Alfons Parczewski, O zbadaniu granic i liczby ludności polskiej na kresach obszaru etnograficznego polskiego (On examining the borders and the number of Polish population in the borderlands of the ethnographic area of Poland)
Jan Drabina Górny Śląsk (Upper Silesia) 2002
I hope this research will be useful in some way.