“Chronological reasoning” means thinking logically about how and why the world changes—or, sometimes, stays the same—over time. While all fields of knowledge offer arguments based on evidence or make comparisons, historians are uniquely concerned about the past and its relationship to the present. How is the world different now from how it was 50 years ago, 500 years ago, or 5,000 years ago? Why did the world change? How have some aspects of the world remained relatively the same over long periods of time? On what basis do historians simplify the long and complicated past by breaking it into smaller eras?

Historical Causation

Causation has to do with explanations about how or why changes take place in world history. Sometimes there is an obvious connection between an event and its consequence, like a cue ball striking the eight ball and making it move. And some events are fairly straightforward: the attack on Pearl Harbor prompted President Roosevelt to ask Congress for a declaration of war against Japan. But even this seemingly simple example is more complex. Why did Japan attack the United States? What role did the American embargo on the sale of oil have on Japan’s decision? Why did the United States enact this embargo? All of these other events took place just a few years before the Pearl Harbor attack. If we go even further back, we’ll gain additional insight about the larger context of the Japanese government’s decision. A longer-term analysis might lead, for example, to an understanding of Japanese imperial aggression as an outgrowth of their rapid industrialization during the Meiji Restoration of the late nineteenth century and a continuing fear of domination by Western powers.

Just as there were many factors behind the Japanese decision to bomb Pearl Harbor, most examples of historical causation involve multiple causes. Historical causation also involves large processes, unintended consequences, and contingencies, as this chart describes.

You can begin to develop the skill of determining causation by asking yourself, whenever some significant change in world history is described, what reasons explain the development. If the answer seems simple, keep digging, because there’s bound to be a more complicated (and longer-term) explanation.

Patterns of Continuity and Change

Historians are interested in both historical changes and persisting patterns, or “continuities.” Change is easier to see: when one empire overthrows another one, that event often becomes part of the historical record. But some things stay relatively the same for long periods of time. Because continuity (such as a network of trade that remains in existence for hundreds of years) is less dramatic than change, it can be harder to spot.

What counts as continuity depends on the scale of time you’re working with. The Soviet Union was continuous throughout most of the twentieth century. However, in the timeframe of Russia’s history since the formation of Kievan Rus in the ninth century, the Soviet era looks more like a short-lived exception.

When historians talk about continuity, they’re not implying that a particular pattern applied to everyone in the world or even in a particular region. Nor are they claiming that absolutely nothing changed in the pattern they’re describing. For example, agricultural production has been continuous for thousands of years. But there are exceptions to this broad statement. On the one hand, some people have continued to be gatherer-hunters; on the other hand, methods of farming have changed substantially with technology. So the continuity of agriculture is a generalization but not a completely unchanging pattern; nor is it a pattern that applies to everyone on the planet.

To work on developing this skill, look for places in your text where an author directly indicates that a historical pattern persisted over time and explains why that pattern persisted. But even when an author focuses on change in world history, you can still find continuity by inference, since few things ever change completely. When the text describes a new development, ask yourself what didn’t change. For example, while Buddhism became popular after its introduction into China, Confucianism remained an important force in Chinese culture.

Periodization

Periodization refers to the ways that historians break the past into separate periods of time. Historians look for major turning points in history—places where the world looked very different before some event than it did after—to decide how to break the past into chunks. They then give a label to each period to convey the key characteristics and developments of that era.

Because the past is complex, particularly when talking about a subject as vast as world history, any attempt to create eras and give those eras labels can provoke disagreement. Some world historians, for example, argue for a major division at 1000 C.E., which would highlight the important role of nomadic peoples in the period between 1000 and 1450. Others prefer to maintain a single period from about 600 to 1450, since they don’t think nomadic empires significantly interrupted a larger period of Afro-Eurasian contact. These disagreements often carry over into the classroom. The AP World History course used to make a break at 1914, instead of 1900; this older periodization made World War I a major turning point. Pushing the period back to the beginning of the twentieth century, as the AP World History course now does, places the war in the context of other important modern developments—including developments less focused on Europe, such as the rise of nationalist movements among colonial peoples.

As you develop this skill, pay regular attention to the chapter you’re in, noting what major era it is described as being a part of, and thinking about what the different labels for that era say about the main “story” of that era, at least according to your teacher, your textbook, or the College Board.