What are two time periods, preferably about ten years apart, where changes happened during that time period that most surprised you?
It is hard to say that changes from periods in the past surprise us because we already know what has happened. However, if we need to talk about history in this way, I would say that the events of the 1920s and the 1930s (which are, of course, ten years apart) seem somewhat surprising.
The 1920s were a surprise in a number of ways. Most importantly, it is surprising whenever social values change radically. The 1920s brought a number of changes in the way people behaved. The coming of the “flappers” is the most visible of these changes. It is also surprising that the people of the US would overwhelmingly pass the Prohibition amendment in 1919, only to ignore that law for most of the 1920s.
The 1930s were a major surprise in that they brought about the Great Depression and a huge change in American government. No one would have predicted that a depression as long and as deep as the Great Depression could have happened. Moreover, it is surprising when the government completely changes its attitude towards something as fundamental as the economy. During the 1930s, the US abandoned its previously hands-off approach to the economy and, instead, started to get involved in practically every area of the economy through the New Deal programs.
These changes can all be seen as surprising.