than double that at 5.5%, but in 1937 during the Great Depression the outer British unemployment rate was 16.1% and the Southern rate was less than half that at 7.1%. The weakening economy and interwar unemployment caused several episodes of social unrest in the region, including the 1926 general strike and the Jarrow March. The Great Depression highlighted the weakness of Northern England's specialised economy: as world trade declined, demand for ships, steel, coal and textiles all fell. For the most part, Northern factories were still using nineteenth-century technology, and were not able to keep up with advances in industries such as motors, chemicals and electricals, while the expansion of the electric grid removed the North's advantages in terms of power generation and meant it was now more economic to build new factories in the Midlands or South. The industrial concentration in Northern England made it a major target for Luftwaffe attacks during the Second World War. The Blitz of 1940–1941 saw major raids on Barrow-in-Furness, Hull, Leeds, Manchester, Merseyside, Newcastle and Sheffield with thousands killed and significant damage to the cities. Liverpool, a vital port for supplies from North America, was especially hard hit – the city was the most bombed in the UK outside London and Hull, with around 4,000 deaths across Merseyside and most of the city centre destroyed. Hull, the worst bombed city outside of London suffered damage to 98% of all buildings, the highest percentage of any town or city. The rebuilding that followed, and the simultaneous slum clearance that saw whole neighbourhoods demolished and rebuilt, transformed the faces of Northern cities. Immigration from the "New Commonwealth", especially Pakistan and Bangladesh, starting in the 1950s reshaped Northern England once more, and there are now significant populations from the Indian subcontinent in towns and cities such as Bradford, Leeds, Preston and Sheffield. Deindustrialisation continued and unemployment gradually increased during the 1970s, but accelerated during the government of Margaret Thatcher, who chose not to encourage growth in the North if it risked growth in the South. The era saw the 1984–85 miners' strike, which brought hardship for many Northern mining towns. Northern metropolitan county councils, which were Labour strongholds often with very left-wing leadership (such as Militant-dominated Liverpool and the so-called "People's Republic of South Yorkshire"), had high-profile conflicts with the national government. The increasing awareness of the North–South divide strengthened the distinct Northern English identity, which,