All of us create discrete units of time within which history supposedly makes sense. We find "really important" events and those anchor the stories we tell. These major events often serve as what historians call turning points: they either started something new or stopped something old, ripped people and states apart or brought them together. Think of how you think about history. If you had to explain to your child, or partner, or friend what the basic course of Western history was, for example, you would probably atomize the last 2000 years into some discrete parts: ancient history (up until the fall of Rome in the 400s AD), medieval history (until perhaps 1492), early modern history (from 1492 until the French Revolution), and modern history (from the French Revolution to your present).
The way we talk about history changes when we reach those moments, but they also affect how we understand the stories we tell.
An example: in modern European history, the French Revolution is almost always discussed as the major turning point, the major breaking point that marks the birth of the modern nation state, of modern history. Historians describe not just French politics, but all of French society before the Revolution as the ancien regime. This "ancient regime" fundamentally breaks in the revolution. Who has power, who wants power, the structure of class/group relations, the structure of politics, civil rights - all of this changed through the revolution. Rare is a book that covers the 1700s and 1800s in France without breaking at the revolution.
For Spain, the birth of "modern" history is a bit later - many people use 1808, when the Napoleonic Wars began, but the "old regime" in Spain persisted in power for a good deal longer. Therefore, there are reams of papers in which historians argue whether Spain was truly modern, whether and when the old regime actually died, etc.
But what happens when we break with accepted divisions? What happens when you begin to argue, as this review essay did, that the Third Reich was not, in fact, a true breaking point and should not be considered as a discrete historical era? What happens when you argue that the interwar period was not, in fact, a separate era but was the connective tissue that connects WWI and WWII? What happens when you argue that American history should not be considered in terms of Presidential regimes, but instead in terms of the history of voting rights?
Graduate school encourages people thinking "out of the box," but I have noticed that most of us tend to simply accept the time divisions that previous historians and textbooks set out for us. I concluded about a year ago that one of the reasons why European historians have such difficulty connecting the Iberian (Spanish/Portuguese) experience with the rest of the Continent is because the periodization does not match very well:
Europe: 1789-1815, 1815-1871, 1871-1914, 1914-1945, 1945-1989, 1989-present
Spain: 1808-1830, 1830-1868, 1868-1875, 1875-1923, 1923-1930, 1930-1936, 1936-1939, 1939-1975, 1975-present
As you can see, almost none of the dates match up. Two major problems are that Spain did not participate officially in either WWI or WWII, and so their experience of the first 45 years of the 20th century were markedly different from that of their continental cousins. But even in the 19th century, Spain was slightly insulated - and though they were going through the same or similar processes as the rest of Europe, the Spanish experience usually came a few years earlier or later, and had somewhat different results.
Sorry for the Spanish history tangent... can you tell I am studying for my doctoral exams??? :-) I wonder how much historians could change people's perspectives if we simply started and stopped the history at different points. Perhaps the next class I get the opportunity to teach, I should try to shake things up a bit.
But don't worry - I won't try to tell them that modern history begins in 32 AD. :-)