The French Revolution was caused by social, political and economic problems. People were in discontent with the king. The first two estates were privileged and the third was very unprivileged and had to pay heavy taxes. The third estate did not get along with the first two.
The answer is Great Depression
The main difference is which part of Europe they came from, and the numbers of immigrants. There were many, many more "New Immigrants'" than old, 20 million people between 1880 - 1920. And the New Immigrants came mostly from southern and Eastern Europe, which meant they were almost all Catholics.
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.
