While beautiful, most of these pieces are primarily ceremonial or intended for generals who would rarely involve themselves on the battlefield†.<p>Almost all of these pieces date from after the unification of Japan under the Tokugawa shogunate (c. 1600). From 1600 to 1850 Japan experienced a stable period marked by very little real armed conflict. During this time, the samurai transitioned from soldiers to what were effectively mid-level bureaucrats. However, unlike most bureaucrats, they managed to retain all of the trappings of a martial lifestyle, including ornate armor, beautiful swords, and the occasional mortal duel. It was during this time of relative peace that these (sometimes ridiculous) fashion pieces developed, somewhat complicated by the tradition of incorporating pieces of much, much older helmets into the "core" of the helmets (one of the helmets in the OP has a core dating from the 14th century, but was significantly embellished later on).<p>†This is generally true of what arms and armor have survived from around the world. The stuff that was actually used rusted away long ago; the highest chance for survival was to have been so valuable that no one dared to actually take it onto a battlefield.