This really comes down to some of history's core identity issues as an academic discipline. What constitutes 'important history' and how that history is presented is a central point of contention. On the one hand, one historian would say that a Eurocentric view of world history stands at the forefront of world history because European affairs have had the greatest impact on the world for many centuries. This is also linked to colonization and European politico-economic domination of the developing world, Eurocentric history is dominant because it is the 'history of the political majority'. Thus European history is more important because it is more influential and central to understanding the world as we know it today. On the other hand, another historian would challenge this idea by asking 'what makes European history more important than say Japanese history'. They would argue that all history, no matter what perspective it is told from is equally valid. This is where social history originates, the idea that history has been told from one perspective for far too long and that the experiences of minorities needs to be heard.

Your world history text book isn't unlike many others out there. Regardless of what you perceive to be the 'proper' or 'better' way of presenting history is, I think it is important that you know and understand the Eurocentric version of world history because it is the most dominant. If you wish to challenge it, you will first need to understand it. I also think that this isn't so bad for secondary level history, which is primarily focused on building your knowledge base and giving you an opportunity to exercise some critical thinking, which I can see you are doing :)

I recommend you read: Richard J. Evans: In Defence of History

which also could explain the reason why Chinese history is being significant part of history class exceptionally; there are tons of Chinese bibliographies we can find

This isn't an answer to your main question, but I just want to address this point above, and it may be related to the question about Europe as well.

There is actually a huge amount of Japanese scholarship on Chinese topics. My own examples are coming from linguistics, but if you really want to get into things like Manchu scholarship or even more general historical linguistics, Japanese sources are quite significant. So in addition to there being a lot written about Chinese history (and I mean that in the broadest sense), there's a lot written about it in Japanese by Japanese historians. It's also a huge area with historical and archaeological records going way back, and in an area very much related to Japanese history and culture. So that being prominent in the text books in Japan doesn't surprise me at all. The history of the region is very accessible, so it's easy to distill into a textbook.

What level are the books for that you're asking about? Something like high school?

edit: yep there it is, clear as day. oops.

I may be wrong but since most of the first world countries are in the westen world, its more likely that thats where the focus is, as many things comes from the ancient european civilizations. Atleast this makes sense for us from europe, as we read a lot more about general european history then about our own history (swedish), or about easten history. For us, we had more then 60% of our textbook focus on the rest of the world, with almost only 20% was about sweden, but then again, this might be casue we are in europe, and there isnt much to be said about swedish history.

Since you are asking about Japan specifically, can I ask a follow-up question?

When did that happen? Was it during the Meiji restoration? Or perhaps after WW2? I assume before that Chinese History would have been heavily studied, as Japan was part of the Sinosphere. And was it a gradual, or an abrupt change?

Is it possible to find contemporary sources explaining why they felt the need to change the textbooks so? That way we would get the reasons "straight from the horse's mouth", so to speak.

High school history also informs future education which is history based. In that sense it is utilitarian.

If you want to study the political sciences, economics, or many of the sciences the history of Europe and the western world is particularly germane to your subject area.

That is not to say that the history of Japan or India or any number of other places is not important, but the foundations of the world economic order and the international system, to say nothing of the rise of the scientific method are all tied to western european history.

If HS history is preparatory for later study that focus makes sense, pedagogically speaking.

It also has a lot to do with the fact that you read a book written in a European language (I presume), probably written by someone of euro descent (or assimilated to that culture) and thus marketed towards your culture as a whole.

If you go to west Africa or China, they are certainly not going to be as interested in Romans and knights and will tell you about their own history. Granted, many around the world are partially "westernized". Westerners most frequently speak to foreigners who are fully or partially westernized (in real life, or through media) creating a selective bias that tends to make Western 1st worlders believe their culture is more widespread and global than it actually is.

And many times, that information about history from elsewhere is either written in another language, or isn't written at all. Lots of history isn't easily accessible in English, as with any other language too.