I'm thinking particularly of the distinctive sloped walls in Japanese castle design, so different from the straight walls used in Europe. I understand that sloped walls are better able to withstand cannon fire than straight walls (explaining the sloped design of the post medieval star forts in Europe) but I believe (correct me if I'm wrong) that the particular Japanese walls were used before the arrival of gunpowder in Japan.
Another difference seems to be the more extensive use of wood in Japanese castle designs, and I'm sure there are many others. I'd love to know more about the reasons behind these quite striking differences.
Thank you in advance.
I've talked a bit about the specifics of Japanese 'castle' building here, but more specifically in answer to your question - due to differences in warfare strategy (mainly that castles pre-Edo were seen as disposable rather than absolute, permanent structures of defence), the overall structure was different. For this same reason, it was easier to make temporary fortifications out of wood than laboriously out of stone. It is important to note the shift in ideologies however as you progress from the Sengoku period into the Edo - as Japan became a unified nation (more or less), there could be spent more time, resources, and energy on building grand castles showcasing the owner's opulence and wealth. For this reason, later castles such as Himeji, whilst representing the same beliefs in design (narrow, winding paths and many gates), were still built with grandeur being prioritised over practicality. Of course, that isn't to say that they wouldn't hold up in an attack, but it certainly wasn't the most important factor.