The correct answer is A. To guarantee American commerce with China. The us sent troops to participate in the multinational force that fought the Boxer Rebellion in 1900 to support U.S. trade goals by helping to preserve China as a nation. The Open Door Policy is a term in foreign affairs initially used for the United States policy in the late 19th century and the early 20th century that allowed for a system of trade in China open to all countries. Recently it is used to open up China to foreign businesses that wanted to invest in the country.
With the Discovery of trench warfare, There was a need for weapons that were capable of long-range destruction and also inflict maximum damage at the same time. this resulted in the invention of many new weapons.
