Should the United States have gotten involved in World War I? Why or why not? What were the advantages and disadvantages?
As pohnpei397 stated, this is largely a matter of personal opinion. I feel that, by the time the US entered the war, it was really the only option.
For most of the war, the US was happy to stay out of it (insomuch as we did not declare war nor provide troops, but we did provide supplies). Public opinion was pretty firm in staying neutral, and President Wilson was very staunch in his own anti-inflammatory policies, seeking to keep American interests as unaffected by the war as possible. He was constantly contradicted by former President Roosevelt, who was incensed by what he felt was a lack of courage on Wilson's part in this and many other diplomatic affairs. The sinking of the cargo/passenger vessel Lusitania prompted Roosevelt to remark that he was "disgusted with our government and with the way our people acquiesce" to its decisions. Despite the fact that he was no longer in office, Roosevelt enjoyed a strong public presence, and he might be considered the leading voice of opposition for the duration of our neutrality.
A great threat to that neutrality was German U-boats. It was in Germany's interest to torpedo any and every ship that it could; this would prevent supplies from reaching England. This, of course, would result in the deaths of Americans, and it was difficult for many Americans to stomach the idea of doing business with England and dying in the process, with no result other than a strongly-worded fist-shaking from our government. We repeatedly told the Germans that "unrestricted submarine warfare", meaning the destruction of any and all ships without warning, would result in a military response. The Germans acknowledged this but, as the war continued and they observed Wilson's ongoing pacifism, they began to doubt our resolve.
The final straw came in the form of Germany's official declaration of unrestricted submarine warfare, as well as the Zimmermann Telegram - a message from the German government to Mexico, encouraging Mexico to declare war on the United States and offering support if it would do so. This made it clear that Germany no longer considered us a real threat, and that peace could not be negotiated. Even if there had been no immediate ramifications for the United States, there would have been irreparable damage to our political power and reputation had we not acknowledged this provocation with a declaration of war; America would be seen as a country of pushovers, uselessly sacrificing its young men to the U-boats and begging Germany for mercy as they died.
This is, of course, a matter of personal opinion. It is also a question whose answer differs depending on the perspective from which you approach it. I would argue that the US should not have gotten involved from a moral standpoint, but that getting involved was largely beneficial to the US from a more pragmatic standpoint.
Although President Wilson portrayed World War I was a war to “make the world safe for democracy,” this was not a war that was about great moral values. It was not a war against aggressive and oppressive dictatorships in the way that World War II was. Germany was, of course, a monarchy, but it was not oppressive. On the other hand, Russia, which was still on the Allied side when the US entered the war, was a monarchy. It was seen as more oppressive and backwards than Germany. The Germans did commit some war crimes, but they were not generally so repulsive as to prove that Germany was evil and needed to be resisted. Therefore, I would argue that there was no moral reason for the US to insist on getting involved in this war.
However, if we are simply talking about what was beneficial to the US, I would argue that it was a good idea to enter the war. From a very cold-blooded perspective, the US did not lose all that much in this war. It entered late so it incurred relatively few casualties. For this relatively (this is not to deny the great pain that these deaths caused those who were involved, but compared to other wars or to other countries in this war, the US did not suffer that greatly as a country) small price, the US gained both economically and in terms of power. The build up for the war enhanced US manufacturing. It helped increase the amount of cooperation between the government and the industrial sector. The US also became something of a world power. It got to have a major role in the Paris Peace Conference. It became a major international power in the years after the war. It is unlikely that these things would have happened if the US had not gotten involved in WWI.
Thus, I would argue that it was not morally important for the US to enter the war, but that it was beneficial in pragmatic ways.
The United States needed to get into the war in order for the Allied powers to defeat the Central powers.
The United States at that time, and still is today, were firm allies of the French and British, especially on issues such as trade. Despite Wilson's stand that the Americans will practice a policy of isolationism/neutrality, the Americans still traded with the French and the British throughout the war. This led to the Germans employing unrestricted submarine warfare, leading to attacks on American trade boats, since the Germans needed to stop the supplies to the Allied forces. As caledon stated above, the public become increasingly angered by the German attacks on American ships. And what pushed them to war was the Zimmermann telegram, which was sent to Mexico asking Mexico to declare war on the United States. This was an attack on American political power, which pushed the US into declaring war.
However, at that time, the British was also trying to get the United States into the war, because they knew that Russia was going to pull out soon (the Russian Revolution was just around the corner and Russia was losing so badly... their soldiers went into battle unarmed), which meant that Germany (probably the strongest power on continental Europe) could put her full force against the French and British on the Western Front, which would mean Allied defeat.
World War I came about from a mess of secret alliances, imperialistic policies, militaristic competition, and nationalistic sentiments. Did the United States have anything to do with European affairs? But because they did participate, the US became the superpower. It all depends on how you feel what the role of the United States should be.