The leader who was in the USA was Jimmy carter. in Britain the prime minister was James Callaghan. However this is because the detente collapsed in 1979 after soviet invasion of Afghanistan.
As per the question however, in the 1980's the USA leader was Reagan and great Britain was Thatcher Margaret.
D. The growing political influence of immigrant groups in the colonies
They resented second class status and wanted more power , felt as if they were being overlooked , they wanted to be the ruling class