World War II changed the planet as we know it forever. According to historians, it was the largest and deadliest war in history, with more than 30 countries sending soldiers to fight for six long, arduous years. The war began with the invasion of Poland by the Nazis in 1939 and lasted until the Allies emerged victorious in 1945. With a war this big and this long, it's no surprise that its pivotal battles were spread out all over the world. Here are four important locations to see if you want to delve deeper into the history of World War II.

Manhattan Project National Historical Park, United States

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The Manhattan Project was the code name of the top secret collection of engineers, nuclear physicists and military personnel who were given the task of producing an atomic weapon during World War II. This led to the scientific field being advanced in leaps and bounds as the group got closer and closer to creating the thing that would ultimately bring an end to the war: the atomic bomb. The Manhattan Project National Historical Park spans three of the "most significant" locations that played a role in the building of the bomb: Los Alamos, New Mexico, Hanford, Washington, and Oak Ridge, Tennessee.

Dunkirk, France

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Movie buffs will recognize the name of this French city from a recent film that depicted the events of "Operation Dynamo," the evacuation of soldiers from French, Belgian, Canadian and British units from Dunkirk. All in all, over 330,000 soldiers were rescued from the Battle of France using both navy boats and civilian vessels in an evacuation that lasted from May 26th to June 4th, 1940. You can visit the sites of this battle today and walk along the same beaches where these soldiers fought to escape with their lives.

Anne Frank House, Netherlands

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When I was growing up, my favorite book was The Diary of Anne Frank. While many people could think of World War II as something that happened somewhere else, to someone else, Anne's diary brought people who weren't born until decades later right into the heart of it, and showed them how the war affected people on a personal, human level. Today, the house in the Netherlands in which Anne and her family were hiding from the Nazis when she wrote that diary has been turned into a museum. You can visit and immerse yourself even more into Anne's world to see where and how she lived before she became another innocent casualty of the terrible war.

Auschwitz-Birkenau Memorial and Museum, Poland

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The most important World War II location on our list is a somber place, a place that should have never existed. Auschwitz-Birkenau was the largest concentration camp built by the German Nazis. Millions upon millions of men, women and children came through this camp, with more than 1.1 million of them dying here. The museum and memorial on this spot hold relics, archives and other artifacts from the war and serve as a way to educate people about the aspects of history that cannot be repeated.