The Potsdam Conference was a meeting that occurred in 1945 among the so-called "Big Three:" Soviet leader Joseph Stalin, British Prime Minister Winston Churchill (replaced on July 26 by Prime Minister Clement Attlee), and U.S. President Harry Truman, in Potsdam, Germany. The three leaders had gathered to discuss how to punish Germany after the war, establish order in Europe, and negotiate treaties.

The Treaty of Versailles, signed in 1919, was a peace treaty that ended the state of war following the devastation of World War I. It made sure Germany accepted all responsibility for damages during the war. The Treaty included provisions stating that Germany had to give back land acquired during the war, that Germany had to pay over 31 billion dollars, and that Germany allowed the countries it had acquired during the war to be sovereign nations included in the League of Nations.

The Good Neighbor Policy, defined by its main principle of non-intervention in the domestic affairs of Latin American nations, was implemented by Franklin Roosevelt's administration in the 1930s. Instead of military intervention in Latin American nations, Roosevelt favored peaceful, reciprocal trade relations with said nations. Both Theodore Roosevelt and Woodrow Wilson had favored military intervention in certain Latin American nations during their presidencies, while Harry Truman and John F. Kennedy were presidents later, during the Cold War, when the US was again starting to take a more interventionist approach in Latin America.

Germany, Austria-Hungary, and Italy were all part of the Triple Alliance. Basically, what that meant, was that all three countries had interloping “aid” treaties; that is, if country X attacks Italy, Germany and Austria-Hungary are going to come help Italy.

Great Britain, France, and Russia were all members of the Triple Entente. This one is slightly easier to remember than the Triple Alliance because the word “entente” is French—clearly, then, the French belong in that group. At any rate, this question is just as important for what it doesn’t ask as for what it does. Note that the question does not ask which countries fought each other in the war; just what countries had overlapping treaties with each other.

The “western front” became a major focal point for WWI (and also was the setting of a novel/memoir by Erich Marie Remarque). WWI was the first time that trench warfare was employed and used so brutally; the western front turned into a “war of attrition,” with either side using gas warfare and tanks to inflict massive injury to the other.

WWI, while rightfully known as one of the deadliest conflicts in all of human history, is also famous (or infamous) for the introduction of new, modern weapons used by both sides. One of the reasons that the casualties in WWI were so astoundingly high was that the development of offensive weaponry--such as the use of poison gas and tanks--had far outpaced military warfare tacticians. In other words, each side of the War had access to new and deadlier technology, but neither side adjusted their warfare tactics to account for it.

The Treaty of Versailles officially ended WWI. The “Big Four” (Italy, France, UK, US) were responsible for crafting the terms of the treaty, and saddled the losers of the war (primarily Germany) with massive reparations. The reparations (repayments for the war, essentially) were so large (both at that time, and even today), that Germany didn’t finish paying them off until 2010.

All of the answers given were correct. The two specific ones—the sinking of the Lusitania and the Zimmerman telegraph—are likely the most important. The Lusitania was a British passenger ship that was carrying American civilians. The Germans, suspecting it of smuggling arms, torpedoed the ship, killing innocents. The Zimmerman telegraph was essentially a telegraph from the Germans to Mexico asking them to join in an alliance with Germany against the US.

This should have been a relatively simple question. The "day which will live in infamy" is a line from FDR regarding December 7, 1941. It was the day that the Japanese attacked Pearl Harbor, and the beginning of the United States' formal involvement in World War II (after a declaration of war from Congress).