Cause scientices need to reason
Shi Huangdi had the Great Wall of China built to protect the Chinese states and borders against the raids and invasions of the various nomadic groups of the Eurasian Steppe. This included the Mongols to the north, which had been very powerful during the rule of Genghis Khan. The other purposes of the Great Wall were border controls, allowing duties on goods during the period of the Silk Road, regulation and encouragement of trade and the control of immigration and emigration.
It declared independence from British parliament and stated the rights all Americans need to have
Answer:
Ever since Columbus set foot in the Americas, the number of endemic species, that is to say, species that only live in a specific geographical area has diminished, while other species have thrived, in the five continents.
For example, the Columbian Exchange led to the cultivation of a South American crop: the potato, across Europe and Asia, where millions of people in cold climates where able to avoid famine by feeding themselves with it.
Another biological homogeneization process occurred with disease vectors: before the Columbian Exchange, diseases such as measles or smallpox were unheard of in the Americas. When Europeans arrived, Native Americans did not have defenses against this illnesses, and the majority of them perished because of contagion (over 90%).
Nowadays, these diseases are present all over the world, but thanks to vaccines, they do not kill as many people as before.
