Significantly, on 21 July 1920, only six days following the publication of the letter above, the outbreak of sectarian violence, known as the Belfast pogroms, began which by 1922 resulted in a quarter of the city's Catholic population (some 23,000) having to flee their homes (Elliott, 2000: 374–5). A few years later during the Boundary Commission hearings (1924–1925), it is evident how, in the absence of a plebiscite, outdated body counts based on 1911 census figures were bitterly disputed in border areas and used to argue for, or to contest, the redrawing of the boundary between the new Irish Free State and Northern Ireland. More recently, an escalation of murders of Catholics followed the release of the 1991 census which recorded an increase in the Catholic population to 42.5 per cent (Elliott, 2009: 245). Clearly, demography has long been a source of anxiety in Northern Ireland; the main concern usually focused on the balance of Protestants and Catholics in the population and the repercussions of this majority/minority ‘body count’ for future governance. Migration affects this cohort balance and significantly it is the demographic factor – the others being birth, death and fertility – over which the government is perceived to exercise actual control. Although official migration policy is administered at the UK level, creation of a climate within Northern Ireland that may either encourage or discourage migration, especially emigration, consequently affects population balance. However, migration in Ireland and Northern Ireland is influenced not only by local factors but by global economic conditions that generate the push and pull demands of labour and international markets. Geopolitical structures and networks are also instrumental in how, when and where migrants relocate. In the case of Northern Ireland, the British Empire/Commonwealth has been the most influential global system that has facilitated migration, first of all through mobility made possible by British nationality; second, by the provision of a travel and shipping infrastructure from British ports and airports; and third, by government assisted emigration schemes.