Answer:
The World War II Memorial sits between the Lincoln Memorial and the Washington Monument and was opened to the public in May 2004. Since that time, it has become one of the most important points of interest located in the National Mall. I believe this is the most important as it shows how history won't repeat itself in such a horrific way.
Although I do have to say that as National Mall has more then 100 unique monuments & memorials, all of them have their own reasons to be there such as the korean war monument, In remembrance of those who fought in the Korean War, the United States Congress confirmed that a memorial be built upon the National Mall on April 20, 1986.
So I cant say which one is my personal opinionated favourite as they all have meanings behind them.
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