Officially, 151 demonstrators were killed and thousands were wounded. In 1912, the Archcathedral of St. Stanislaus Kostka was completed and its tower at is one of the tallest in Poland. Despite the impending crisis preceding World War I, Łódź grew exponentially and was one of the world's most densely populated industrial cities, with a population density of by 1914. In the aftermath of the Battle of Łódź (1914), the city came under Imperial German occupation on 6 December. With Polish independence restored in November 1918, the local population disarmed the German army. Subsequently, the textile industry of Łódź stalled and its population briefly decreased as ethnic Germans left the city. Restored Poland (1918–1939) Despite its large population and economic output, Łódź did not serve as the seat of its province until the 20th century. Following the establishment of the Second Polish Republic, it became the capital of the Łódź Voivodeship in 1919. The early interwar period was characterised by considerable economic hardship and industrial stagnation. The Great Depression and the German–Polish customs war closed western markets to Polish textiles while the Bolshevik Revolution and the Civil War in Russia put an end to the most profitable trade with the East. Because of rapid and, consequently, chaotic development in the previous century, Łódź did not possess the adequate infrastructure and living standards for its inhabitants. Pollution was acute, sanitary conditions were poor and the authorities did not invest in a sewage treatment system until the 1920s. From 1918 to 1939, many cultural, educational and scientific institutions were created, including elementary schools, museums, art galleries and public libraries which prior to the First World War did not exist. Łódź also began developing an entertainment scene, with 34 movie theatres opened by 1939. On 13 September 1925, the city's first airport, Lublinek, commenced operations. In 1930, the first radio transmission from a newly-founded broadcasting station took place. The ideological orientation of Łódź was strongly left-wing and the city was a notable centre of socialist, communist and bundist activity in Polish politics during the interbellum. Second World War (1939–1945) During the invasion of Poland in September 1939, the Polish forces of General Juliusz Rómmel's Army Łódź defended the city against the German assault by forming a line of resistance between Sieradz and Piotrków Trybunalski. The attack was perpetrated by the 8th Army of Johannes Blaskowitz, who encircled the city with the X Army Corps.