The correct answer to this open question is the following.
Although there are no options attached we can say the following.
The Open Door policy attempted to preserve the chances for American businesses to enter which markets?
Answer: in the market of Asia, specifically, in China.
At the end of the 1800s and the beginning of the 1900s, the United States wanted to improve its trade relationships with Asian countries, especially with China. The United States knew that some European nations had some previous trade relations with this country and had some kind of preferences. The United States federal government did not want to be left behind in trade with China, and that is why it formulated the Open Door Policy to close good deals and improve trade with China.
Signs point to North Korea unilaterally launching the invasion. It was not helpful for the USSR and was at a very bad time for the PRC since the war immediately shut down plans to invade Taiwan.
The U.S., especially after Chinese troops entered the war, viewed it as a united and aggressive communist bloc brashly taking over one more country and likely to try more if not resisted. US defense spending shot back up to wartime levels (though far from the WWII peak) and stayed there.
China also viewed it as a feeler for aggression that would go further if not resisted. Both countries were overinterpreting local issues as global ones.
The dramatic reverses were all in the first year, followed by two years of stalemate before the armistice.
Martin Luther King assasinated, Robert kennedy wounded.
