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).

By the beginning of 1917, the War in Europe was in a long stalemate, but America had not yet joined in despite being strongly favored towards the Allied powers of Great Britain and France, largely thanks to German wartime policies such as U-boat attacks on neutral ships. In January of 1917, a secret message from the German foreign office to the government of Mexico, known as "The Zimmerman Telegram," was discovered. In it, the German government suggested a military alliance that would seek to return the American Southwest to Mexico. This factor directly sparked the American entry into World War I.

Wilson’s Fourteen Points speech was delivered months after the United States entered the war on behalf of the Allied Powers in April of 1917.  Facing political blowback about reasons for joining a nationalistic war, Wilson constructed a pro-war argument based around the need for a new form of diplomacy post-war and sovereignty for specific European populations.

First used in a speech before he assumed the presidency, Theodore Roosevelt's Big Stick diplomacy was his belief that intelligent forethought must be coupled with military muscle.

The so called “Truman Doctrine” argued that it was the responsibility of the post-war United States to support the extension or maintenance of freedom, personal liberty and democratic ideals throughout the world. The quote comes from a speech given by Truman, to Congress, when he was calling for funds to support those people in Turkey and Greece who favored democracy. 

The Nye Report was a Senate report issued during World War One that stated that American banks and corporations had tricked the American people into supporting a war so that they could gain profit from the sale of arms, post-war reconstruction projects and the elimination of foreign competitors. The report was widely quoted as a very significant reason for avoiding conflict in Europe and Asia in the 1930s and persisted into the early 1940s, as a reason not to join World War Two on the side of the allied forces

The correct answer is Grover Cleveland. Taft, Roosevelt and McKinley all initiated conflicts or invasions that advanced American interests abroad. All three believed that the United States needed to expand its influence around the world to serve national interests. Wilson, who was staunchly against European Imperialism and ideologically opposed to America’s interference in foreign nations, still managed to send American troops into Nicaragua in 1914 to occupy the country and Haiti and the Dominican Republic in the years immediately after. Thus, Wilson can be seen as an Imperialist in practice if not in ideology. Grover Cleveland, on the other hand, came to the Presidency in the years shortly before Imperialist ideology took over the office, and once out of office he was a devoted member of the American Anti-Imperialist League. The Anti-Imperialist League believed that Imperialism violated the republican principles that America had been founded on, and they fiercely objected to any forced occupation of foreign lands.