Answer:
What is the U.S. "Open Door" policy?
A policy proposed by the US in 1899, under which ALL nations would have equal opportunities to trade in China.
Why was it declared?
It was declared with the intention of protecting the rights of all countries to trade equally with China and confirming the multinational recognition of administrative and territorial sovereignty.
How did China under Guangxu try to modernize?
The changes ranged from infrastructure to industry to the civil inspection system. The Guangxu Emperor issued decrees allowing the establishment of a modern university in Beijing, the construction of the Lu-Han railway, and a budget system similar to that of Western governments.
How did this lead to the Boxer Rebellion?
In 1900, however, internal events in China threatened the idea of the Open Door. An anti-foreign movement known as the Boxer Rebellion, named for the martial artists that led the movement, gathered strength, and began attacking foreign missionaries and Chinese converts to Christianity.
hope this help! ^^