16 History ID's

The identifications should each be about a paragraph in length (not just one sentence!). In the paragraph you should explain, if applicable, who is involved, what happened, where it happened, and when it happened. Most importantly, tell me why the identification term is important in a greater historical context. I want to know how it fits into history and why we are talking about it.

I need to see it written from the perspective of (or even saying) "X is _____, and it is important because _____."  How did it affect society?

Identifications:

“sick man of Europe”

Lusitania

Treaty of Versailles

League of Nations

Russian Revolution

Mao Zedong

D-Day

Holocaust

Hiroshima/Nagasaki

Iron Curtain

North Atlantic Treaty Organization (NATO)

Marshall Plan

Truman Doctrine

Doomsday Clock

Balfour Declaration