Nonliterate cultures are actually very well within the scope of history, it simply takes more effort than reading documents in a library.

I will give you a hypothetical example; I would cite something that really happened but I don't have the luxury of time (I have to pack for vacation basically right now).

Say there is an isolated tribe of North Africans who have had no written documents about them, ever. Period. Zero documents. They rely entirely on an oral record. Now, as a historian, you are attempting to discover the history of the tribe prior to the 1900s, when documents about them were made by the French as part of their colonization efforts in the area. So what do you do?

First and foremost you visit the tribe and listen to their oral record, from a variety of sources. Let's say this tribe is about thirty thousand people in all, and three hundred of them are considered knowledgeable in the history of the tribe and its oral tradition. So, over the course of some time, you listen to the entire oral history of the tribe from a good statistical sample of all 300 orators. You then take all of these versions and compare them with each other. What events are consistent across the board? What only have minor differences, and what is told only by a handful of the sample? Let's say you narrow it down and for the purposes of the hypothetical example, you find three major events that are generally agreed upon as having occurred in the way told.

The first is the slaughter of the tribes Great Leader before they were nomadic by what are described as "silver-red devils." The second is the arrival of Screaming Men on Horses, and third is trading gold for guns with the blue-coated men who are described as not being from across the sea.

You can safely assume that these three events occurred in some way, shape, or form. There is nothing mystical about the events, not really, and the events do not rely upon anything magical or out of the realm of possibility. Before you can comment on what the events likely are, you must first compare them to what you already know.

So you know that Roman armor was iron (silver colored) with red cloth or paint. And you can check by the general age of the tribe, its lifespan, and how many generations ago the event occurred (statistically averaged of course) to see if it matches up with the Roman Empire's incursions in to North Africa. Let's pretend that it does.

Second event coincides with the Arabic invasion and is also right around the time mention of a polytheistic dynasty tends to stop; let's say you notice a trend that less and less events are explained through mysticism when the screaming men arrive. This is likely the Arabic conquest of North Africa, and so you chalk it up to that.

The third event has you confused initially. Blue coats imply the French, but the French have no documented evidence of ever meeting a nomadic tribe in North Africa at the time described. So you go to your reference and check for all countries that have blue uniforms at the time, as well as any mercenary companies or smaller nations that had bought blue uniforms even if they weren't standard issue. In the process, you realize that the United States had blue uniforms at the time, and so you cross-check the date with your timeline of United States history and find that it occurred very close to the U.S. retaliation against the Barbary pirates.

You then check further in to records of ships and discover that a Captain was fined a year's salary for trading a small stock of gold taken from Tripoli to a tribe of "desert Arabs" when the ship stopped for a quick resupply. The description of the tribe is similar to the traditional garb worn by the nomadic tribe you are trying to understand.

Thus, you can safely assume that the tribe has had three major interactions with other areas. They were 1. Invaded by the Romans, 2. Conquered and converted by the Arabs, and 3. Had contact and were introduced to firearms by the Americans.

Yes, this is a hypothetical example and thus of course leads to that conclusion. Field work would not be that easy, and at times would probably require the help of an anthropologist. But, you are still able to determine to a pretty high degree of certainty just how valid an oral tradition is. This has actually been a thing in history for more than two decades; the acceptance of oral tradition was kicked off by the revisionist movement to a much more thorough degree than it had in the past and it really did bring a much more broad perspective on the subject. The view of history as solely a written tradition is very, very outdated in the field.

That being said, you are confusing history with a straight line in the first part of your post. Hegel -/-> Marx. Hegel + Social Conditions + Burgeoning German Identity + Rise of Industrial Society + everything else happening at the time = Marx. It is not Hegel leads to Marx with nothing in between. Its Hegel leads to thousands of other things, some of which connect to Marx, but also connect to American Capitalism, to Bismarck, to basically everything. Its not a straight line so much as a gigantic web of connections between people, technology, and events, and trying to classify a part of this tapestry as "intellectual history" is assuming operation in a vacuum when operating in a vacuum is impossible.

History is a study of the events and connections. By its nature, it avoids straight lines. Just look at JFK for a little brief example. JFK wins the presidency because he comes in at the right social time (postwar boom), has the right image for the public (young, hip, energetic), and looks good on television (as compared to Nixon.) But why were the social conditions like that? What had shaped the public desire? Who had created that concept of good looks, and who brought about the television as a means of delivering media? Answer those questions and you have history.