Because it could roll over bombed out landscapes and keep penetrating the opposing force. Hope that helped! ;)
The Corps of Discovery refers to the military unit that took a two year expedition with Lewis and Clark in order to explore the land recently bought by the US government from France. This territory became known as the Louisiana Purchase.
When exploring with Lewis and Clark, the Corps of Discovery went through several different states that exist today. This includes Kansas, Nebraska, Montana, Idaho, and Washington. Essentially, this route went from Missouri to the Pacific Ocean in Washington, covering the middle of the continental US all the way to the Northwest corner of the US.
Open Door policy. Open Door policy, statement of principles initiated by the United States in 1899 and 1900 for the protection of equal privileges among countries trading with China and in support of Chinese territorial and administrative integrity.