Look it up fool. Morning stars, and Flails are not the same thing. They are related in design, and origin. But nonetheless very different weapons. Morning Stars were designed for a higher class of warrior, the Knight. The way it is made is to maim an enemy so that it makes it harder to fight back. Flails were improvised weapons made up of everyday farm tools that were meant for threshing. They were essential weapons in revolutions against land barons. These were designed to kill. Throughout the world you can see many types of Flails. Even Asians used similar weapons.
Get it? Morning Stars are a strategist's weapon of choice. It could destroy shields, at the same time break bones. The Flail was the peasant's(foot soldiers and such) choice of weaponry. They could storm the gates of enemies, and kill them from a safe distance (much like a Lance or Hal-bred). Epic flail by the way. Where did you get the picture? I especially like this one.
the weight and balance of a naginata blade is totally different from a katana - the blade shape is broader at the tip. I trained in aikido, which took a great deal of its strategy from medieval Japanese women's warrior training with naginata. A beautiful weapon, close to my heart, along with the glaives and halberds that have been getting much love.
on a related note, you might enjoy this documentary - it talks a bit about the influence and connection between damascus steel swords and viking swords...
http://www.pbs.org/wgbh/nova/ancient/secrets-viking-sword.html