I would have to say that the Japanese were fundamental in shaping all the nations of Asia through trade or conflict. (Maybe not as much so as China influenced Japan, but the Japanese have influenced China as well.) I do not mean to be disrespectful or callous, but the implications and consequences of some of Japan's military struggles with the eastern world set the foundations for the people's of those nations to rise up against oppression and tyranny. At least, that's the way I look at it. Every act, no matter how violent, can have unforseen positive consequences down the road. Every cloud has a silver lining, so to speak?

Ah, but you meant something tangible. In all honesty? Nihonto. The Japanese sword is a marvelous instrument as well as a piece of functional art. Think of how deeply the katana, tachi, daitō, and wakazashi just to name a few have shaped Japan and even more so, what we and the rest of the world see in modern culture. I also like to look at how the Japanese adapted to using the early period chokutō, or chinese swords.

I mean, one of the three imperial regalia is the Kusanagi-no-Tsurugi.

But I see it as a "contribution" to the world because it can be appreciated, and because of all the old Samurai films it inspired, not to mention contemporary films use it and have crafted an entire lore around it.

The nihonto gave George Lucas the idea for the lightsaber (and the Samurai
gave him the idea for Jedi.)

Japanese art is what inspired me to become an art/antique appraiser, so I can hopefully own my own business. So I definitely think the nihonto is a valued contribution.

Woo, first post!