The first civilizations didnt use metal very often, but when they did it was usually for farming tools.
Emperor Meiji finally achieved to get over the ancient and previous traditions of Shogun Lords, which lasted almost 800 years. With, the Meiji restoration, the country formerly established relations with powers in Europe, the United States, and other parts of the world. This became key "in putting Japan into the scene", in the international community. The ancient practices were not fostered anymore (based on Cultural and social distinctions ). It can be said that the nation had formerly consisted of huge differences to be considered relating what people have as an office, the status they served, etc.
So Japan finally entered the modern world, after a long series of wars that were targeted to maintaining the cultural unity and a policy of isolationism that also resulted in upgrading and incorporating changes in Japan foreign policy and structure of the military.
I would say all of the above except the last option. "Dirty conditions led to disease "
<span>The interaction between imperial china and central Asian nomads change after 1100 CE. This was the blooming of China's civilization and its venture into the political world and inevitably expanding its territories to Central Asia. In return, China became the center point for politics and economy on that era.</span>
