In the 1500s a new type of armor started to become popular due to the advent of firearms, new fighting tactics and the need for additional protection. The kozane dou made from individual scales was replaced by plate armor. This new armor, which used iron plated dou (dō), was referred to as Tosei-gusoku, or modern armor. Various other components of armor protected the samurai's body. The helmet kabuto was an important part of the samurai's armor. Samurai armor changed and developed as the methods of samurai warfare changed over the centuries. The known last use of samurai armor occurring in 1877 during the satsuma rebellion. As the last samurai rebellion was crushed, Japan modernized its defenses and turned to a national conscription army that used uniforms.
Try to answer this question if possible (otherwise reply "unanswerable"): Why were there armor changes in the 1500s?
the advent of firearms, new fighting tactics and the need for additional protection