Battle of Beresteczko between Poles and Ukrainians began: After a two-year truce, the Battle of Beresteczko was fought between the Ukrainian Cossacks, under the command of Khmelnytsky, aided by their Crimean Tatar allies, and a Polish army under King John II Casimir. A total of 33,313 Cossacks, supported by Ukrainian peasants, went into battle against the Polish army. By mid June 1651, the Polish army numbered 14,844 Polish cavalry, 2,250 German-style cavalry, 11,900 German-style infantry and dragoons, 2,950 Hungarian-style infantry (haiduks), 1,550 Lithuanian volunteers, and 960 Lipka Tatars. In addition, there were also 16,000 German mercenaries, and a few Cossacks who were loyal to and remained within the ranks of the Polish army. The Polish commanders planned to break the Cossack ranks with a charge of the Polish Winged Hussars - an effective, and deadly tactic that had been used in many previous battles, such as at the Battle of Kircholm and Kłuszyn. (It would later prove victorious in the famous 1683 Battle of Vienna against the Turks.) The Cossack army was already well acquainted with this Polish style of war and chose to avoid an open battlefield by fighting from a huge fortified camp. During the first day of fighting, the Polish Winged Hussars emerged victorious,"since their army sustained that first attack cheerfully and in high spirits". The Polish Winged Hussars were victorious on June 30, 1651.
The Treaty of Versailles was signed bringing World War I to an end. (It was signed exactly five years after the assassination of Archduke Franz Ferdinand. Article 231 of the Treaty, later became known as the War Guilt clause, forced Germany to disarm, to make substantial territorial concessions, and to pay reparations to certain countries that had formed the Entente powers. Among the terms and conditions of the Treaty was that Germany recognize the independence of Poland and renounce "all rights and title over the territory". Territories to be ceded to Poland were parts of Upper Silesia (with the future of the rest of the province to be decided by plebiscite); the province of Posen (now Poznan); Pomerelia (Eastern Pomerania), on historical and ethnic grounds, so that Poland would have access to the sea, ie the Polish Corridor; the East Prussian Soldau area; (while the sovereignty of southern part of East Prussia would be decided by plebiscite); and the city of Danzig ( became the Free City of Danzig, established by the League of Nations.) An area of 51,800 square kilometres (20,000 square miles) was granted to Poland. Memel was to be ceded to the Allied and Associated powers.
Four Crematories at Auschwitz: SS Major Karl Bischoff, chief of construction of Auschwitz II-Birkenau, had implemented the construction of the four crematories by the end of June 1943. Crematory I was a brick cottage with windows sealed, and converted into a gassing facility. Crematory II was converted a few weeks later. Crematory III used an existing mortuary with morgues in the basement and ground-level incinerators, and converted it into a killing factory by installing gas-tight doors, vents for the Zyklon B (a highly lethal cyanide-based pesticide) to be dropped into the chamber, and ventilation equipment to remove the fumes afterward. Crematoria IV & V were designed as gassing centers, were also constructed that spring. By June 1943, all four crematoria were operational. Most of the prisoners were killed using these four structures.
The Heuaktion (or hay operation) was a Nazi German operation in which they kidnapped 40,000 to 50,000 Polish children from the ages of 10 to 14 and transported them to Germany as slave labourers. Upon their arrival in Germany, the children were handed over to Organisation Todt and the Junkers aircraft works. The Nazis expected that the mass kidnapping would pressure the adults of the occupied territories to register as workers in the Reich, as well as to weaken the “biological strength” of the areas of the Soviet republics which Germany had invaded. (After the end of World War II, the Nuremberg Trials classified the kidnapping of children as part of the Nazi program of systemic genocide.)
Under the terms of the Yalta agreement, the Provisional Government of National Unity (Polish: Tymczasowy Rząd Jedności Narodowej or TRJN) was formed to govern Poland until free elections could be held and a permanent constitutional system established. Former Prime Minister of Poland Stanisław Mikołajczyk trusted the Soviets and entered into negotiations with them, but would later be betrayed. The Polish Government-In-Exile did not recognize the TRJN.
Riots broke out in Poznan Poland, 38 died: Workers demonstrated to demand better working conditions at Poznań's Cegielski Factories and were met with violence. Over 100,000 workers gathered in the city centre near the local Ministry of Public Security building. About 400 tanks and 10,000 soldiers of the People's Army of Poland and the Internal Security Corps under communist officers were ordered to suppress the demonstration and during the pacification fired shots killing many of the protesters. Casualties were estimated between 57 and 100 people or more (including a thirteen-year-old boy, Romek Strzałkowski.) Hundreds of other demonstrators sustained injuries. The Poznań protests were a milestone in the Polish struggle leading towards the installation of a less Soviet-controlled government in Poland in October.