So, as /u/Randomname64 points out, youd have to first define 'microhistory' vs. 'macrohistory.' What, exactly, is a microhistory? In the field, the term microhistory generally means a very small history which focuses on a person or small group of persons, generally of a common sort. These stories, such as The Cheese and The Worms or The Return of Martin Guerre focus on telling a very small story, but that (usually!) tells us something about the larger state of society at that point. A Macrohistory would be something like Ferdinand Braudel's The Mediterranean and the Mediterranean World in the Age of Philip II which attempts to explore the social and economic developments of the entire Mediterranean basin during the 16th century. Pretty big stuff. You could probably also plop Livy's history of Rome or Gibbon's The Decline and Fall of the Roman Empire. Though Id be wary of assigning modern categorizations to books which are hundreds (or in the case of Livy, thousands) of years old.

But in between two kinds of books you have a lot of topics. In fact, I think its fair to say most historical scholarship would fall in between those two distant positions. And it goes back to defining your original question: Is a biography of Otto von Bismark a microhistory or a macrohistory? After all, by definition a biography is a kind of microhistory, youre only focusing on one person! But Bismark is a pretty big person who shaped the development of an entire continent. In reality, I dont think either term really describes what that book is. Nor do they describe works Im more familiar with, such as campaign histories. Is a book on the Six Day War a microhistory? I doubt most 'microhistorians' would agree with that point, but in terms of chronology, that book probably spans a shorter period of time than almost any other!

Your second question, I think, is really what youre asking. That is, why does social, economic, and cultural history seem to be the most popular forms of history these days. Well, first of all Id just like to say that we diplomatic, political, and military historians are doing just fine, thank you for asking. Second, we need to look at what the field of history was like when we diplo-politico-military historians 'ruled the roost.' That is, the topic of many of these histories focused on a specific subset of Amero-Europeans. These people were old, rich, white, men who were in powerful and connected positions. This makes a lot of sense, given that these men were out front making the diplo-politico-military decisions which swayed nations and drove the broad development of Europe and America.

But these histories had a major flaw: they only looked at one part of a big picture. I dont know if youre familiar at all with American history, but ask this question: where would the United States be with Africans brought over as slaves? If you only understand the 19th century through the lens of John C. Calhoun, Robert E. Lee, and Abraham Lincoln you are missing out on a lot of different people, people whose experiences also drove history. And think about women, half of the human population are women. What role did they have in the development of society?

The rise of social and cultural history especially shifted the focus away from studying the masculine half of the 1% (to steal a hot phrase). Instead, it asks 'what were the 99% up to? What did they think, say, feel, do during this period?' To answer this question, it requires a radical shift in how historians have approached their subject. To go back to a previous example, how do you study the experience of African slaves, many of whom could not read or write? What kinds of sources are available to those historians? The field has expanded in these areas because there are a lot of stories to tell, but also because there are a lot of questions to be answered. We live in a generally pluralistic society, where everyone get to have a voice. Socio-cultural history aims to give these people, and their historical antecedents, that voice. And its no coincidence that this field of history developed following World War Two, when all sorts of gender, ethnic, and sexual (etc.) minorities gained a new voice in society. History had to expand because society expanded. Those kinds of histories I like, those which focus on the battles, campaigns, and political machinations of the great and powerful arnt gone. Theyre as alive and well as ever. But they exist next to a whole group of histories which seek to complicate those stories, when they arnt telling entirely new ones! And a lot of the 'old' kinds of history are themselves adapting to incorporate a broader, and more accurate, understanding of history. We do not live in the 19th century anymore, and as a result we historians cannot write like we did. We have to write for the 21st century, to help tackle 21st century problems, and to relate to 21st century people.

At least thats my understanding. A question like this is, perhaps, a little too big for a Reddit answer. I was asked something similar for one of my Qual questions a few years ago.

Has there been a major focus on microhistory though? And what do you mean by this? Do you mean a focus on a short period of time (how short?) and a small location (how small?)? There clearly have been some famous examples of this that are radically interesting -- The Cheese and the Worms comes to mind as does The Great Cat Massacre, but I am not so sure they are representative of history. I'm used to reading works that either span a broad geographic location but over a short time (e.g. the League of Nations in The Guardians) or long term cultural histories (e.g. Inventing Eastern Europe) or even global histories (The Birth of the Modern World) comes to mind.

With that said, there might be some incentive to focus on particular subjects because 1) sometimes there are major questions that have very short time periods associated with them (e.g. the causes of WWI; the timing of the Holocaust; the causes of the French Revolution) and 2) to write a big history one will almost certainly have to rely on a number of secondary sources and so your work might be seen as synthetic rather than posing a new focused question. Simultaneously, histories that are "too big" might very well transform into histories of empire, great men, etc. and so people who favor a history of the everyday (Alltagsgeschichte) might favor smaller units of analysis. And one of the streams in the new social history was Alltagsgeschichte, but on the other hand, you also have new social historians like Hobsbawm whose global history can hard be called micro (the Ages series).

But I'm still not sure that there has been much of a change. About four years ago, a book came out called The History Manifesto that broadly made the argument that historians had stopped focusing on long term history (the longue duree, sorry not French) and instead focused too much on short time, human length histories. But, Cohen and Mandler, I think, made a pretty good argument that this is not so. That if we look at monograph production reviewed in the AHR (which seems legitimate, since it is the most important journal in the American historical discipline) we will find that there has been a steady increase in the years historians study. That in 1926, the mean was 50 years, but that by today (well 2006), the mean became 79 years. The authors of The History Manifesto have a reply and I think they kind of miss the point (I say this as someone sympathetic to many of their claims), because they seem to show that there has in fact been a rebound in longue duree history from the 60s onwards according to multiple metrics, where the average history rather than being around 5-50 years, is in fact closer to 60-70 (contra to their initial claim). So, if anything, historians have been dealing with greater periods of time rather than smaller since the 60s.

With that said, I think one response is that I've misread your question a bit. You mention a "history of ancient Greece, Rome, the crusades", etc, but that seems to be quite a bit bigger than 70 odd years. The history of Rome is what a millennium (warning, not a historian of antiquity). That's pretty long. My thought (backed by the data from both by Armitage and Guldi and Cohen and Mandler) is that works like these have generally been rare (if you look at monographs, journal articles, doctoral dissertations) and have generally been the subject of synthetic works or textbooks. But I do not buy that histories that are less than a few centuries are microhistories. It seems to me that microhistory normally refers histories of a very small scale (a village, a workshop, etc.) and a short period, but a work such as say The Sleepwalkers even though it covers a very brief time, doesn't seem to be of a small scale at all.

So, if you interested in those broader works, it's probably worth it to check out textbooks on it, but on the bright side, the average length of time dealt with by monographs, journal articles, and dissertations is rising!

"The History Manifesto: A Critique", by Cohen and Mandler. "The History Manifesto: A Reply to Deborah Cohen and Peter Mandler", by Armitage and Guldi. Both in the AHR. You can grab the whole exchange here. The History Manifesto is also freely available on line.