What do we know about Macroeconomics that Fisher and Wicksell did not?

The answer to the question in the title is: A lot. In this essay, I argue that the history of macroeconomics during the 20th century can be divided in three epochs: Pre 1940. A period of exploration, where macroeconomics was not macroeconomics yet, but monetary theory on one side, business cycle theory on the other. A period during which all the right ingredients, and quite a few more, were developed. But also a period where confusion reigned, because of the lack of an integrated framework.