1920s: Many in Europe are convinced that it is only a matter of time before another war breaks out on the continent. The prospect of war is connected to the fact that Germany resents the harsh conditions imposed on it in the Treaty of Versailles in 1919.

Today: Having endured two major wars in the twentieth century, Europe is now involved in a network of economic and political relationships within the European Union that make a war between the principal powers of France, Britain, and Germany unlikely.

1920s: In 1920, there are 7.5 million cars and trucks in the United States. The rise of the automobile industry in the United States and Europe leads to the development of infrastructure (new roads) and the decline of other modes of transportation such as horse-drawn vehicles, bicycles, streetcars, and interurban trains. Cars change everyday life for millions. Travel becomes easier...