In the early 20th century Glasgow was becoming less of a migrant city. In 1911 almost 62 per cent of the inhabitants were Glasgow-born; forty years later the figure had risen to just over 74 per cent. Of course, during this time definitions of Glasgow altered, as major boundary expansions in 1912, 1926 and 1938 more than tripled the city's territory. Populous communities like Govan and Partick, originally in Lanarkshire, came to be firmly identified as part of Glasgow. By 1951 the city accommodated over a fifth of Scotland's total inhabitants and almost 92 per cent of this number were Scottish-born. Adjacent counties, notably Lanarkshire, contributed the largest proportion of Scottish incomers.
During the First World War demand for munitions' workers had an impact on migration patterns. For instance, in 1916 one Glasgow factory recruited 200 women from the Outer Hebrides to help with shell production. After the war the outflow of Highland population intensified and Glasgow continued to absorb migrants from the north. The Highland exodus also contributed to the extraordinary levels of overseas emigration from Clyde ports during the 1920s, fuelling fears that Scotland's "life blood" was seeping away. Some writers and politicians exacerbated insecurities about national deterioration by suggesting that Irish immigrants were filling the population vacuum. Yet while the Irish remained Glasgow's largest non-Scottish migrant group during the inter-war years, their numbers were in fact diminishing. By 1951 English-born inhabitants (at 3.39 per cent) had marginally overtaken the Irish (at 3.16 per cent).
The Gorbals undoubtedly was the city's most cosmopolitan area. The Irish language, spoken by Donegal-born residents, could be heard alongside Yiddish, spoken by older members of the Jewish community. However, the settlement of "alien" immigrants was generally more difficult from 1919 when work permits were legally required. This affected the movement of groups like the Italians, although inter-war Glasgow still had Britain's largest Italian community outside London. On the other hand, social and political dislocation in Europe brought many refugees, especially from the 1930s. During and immediately after the Second World War there was a dramatic rise in the number of Glasgow's Poles. British decolonisation after 1945 had the further effect of attracting Commonwealth immigrants, especially from the Indian sub-continent.