British Museum Plan

New century, new building (1900–1925)
Opening of The North Wing, King Edward VII's Galleries, 1914

Sir Leonard Woolley holding the excavated Sumerian Queen's Lyre, 1922
By the last years of the 19th century, The British Museum's collections had increased to the extent that its building was no longer large enough. In 1895 the trustees purchased the 69 houses surrounding the museum with the intention of demolishing them and building around the west, north and east sides of the museum. The first stage was the construction of the northern wing beginning 1906.
All the while, the collections kept growing. Emil Torday collected in Central Africa, Aurel Stein in Central Asia, D.G. Hogarth, Leonard Woolley and T. E. Lawrence excavated at Carchemish. Around this time, the American collector and philanthropist J Pierpont Morgan donated a substantial number of objects to the museum, including William Greenwell's collection of prehistoric artefacts from across Europe which he had purchased for £10,000 in 1908. Morgan had also acquired a major part of Sir John Evans's coin collection, which was later sold to the museum by his son John Pierpont Morgan Junior in 1915. In 1918, because of the threat of wartime bombing, some objects were evacuated via the London Post Office Railway to Holborn, the National Library of Wales (Aberystwyth) and a country house near Malvern. On the return of antiquities from wartime storage in 1919 some objects were found to have deteriorated. A conservation laboratory was set up in May 1920 and became a permanent department in 1931. It is today the oldest in continuous existence. In 1923, the British Museum welcomed over one million visitors.
Disruption and reconstruction (1925–1950)
New mezzanine floors were constructed and book stacks rebuilt in an attempt to cope with the flood of books. In 1931, the art dealer Sir Joseph Duveen offered funds to build a gallery for the Parthenon sculptures. Designed by the American architect John Russell Pope, it was completed in 1938. The appearance of the exhibition galleries began to change as dark Victorian reds gave way to modern pastel shades. However, in August 1939, due to the imminence of war and the likelihood of air-raids, the Parthenon Sculptures, along with the museum's most valued collections, were dispersed to secure basements, country houses, Aldwych Underground station, the National Library of Wales and a quarry. The evacuation was timely, for in 1940 the Duveen Gallery was severely damaged by bombing. Meanwhile, prior to the war, the Nazis had sent a researcher to the British Museum for several years with the aim of "compiling an anti-Semitic history of Anglo-Jewry". After the war, the museum continued to collect from all countries and all centuries: among the most spectacular additions were the 2600 BC Mesopotamian treasure from Ur, discovered during Leonard Woolley's 1922–34 excavations. Gold, silver and garnet grave goods from the Anglo-Saxon ship burial at Sutton Hoo (1939) and late Roman silver tableware from Mildenhall, Suffolk (1946). The immediate post-war years were taken up with the return of the collections from protection and the restoration of the museum after the Blitz. Work also began on restoring the damaged Duveen Gallery.