Why did the U.S. enter WWI?

Ok, let's first deal with some of the rubbish from earlier answers.

1. The RMS Lusitania was a British ship flying a British flag. The Germans had said much earlier that any ships flying a British flag were fair game. There were only 128 Americans on-board out of about 1600. The ship was sunk in 1915. USA entered the war in 1917.

2. The Lusitania sinking was not the main reason the USA joined the war but was simply ONE of the reasons. The USA demanded the Germans stop sinking passenger ships. The Germans stopped (for a while)

3. The USA pursued a policy of isolationism (surprise, surprise) and wanted to keep out of the war.

4. Pearl Harbour was in WW2 not WW1.

5. There were no Nazis in WW1.

Why did the U.S. enter WWI?

1. It was starting to look like Germany was going to be defeated. The USA wanted to be part of the post war carve up and wanted to be there for their share of the pie.

2. The USA was supplying war materials to the allies. They could not do this and be "neutral" as well. In fact the USA was breaking international law by supplying the allies.

3. German agents committed two acts of sabotage on war materials in the USA destined for the trenches of Europe.

4. American public opinion was slowly turning against Germany and the public believed the USA should help France and Britain.

5. The American military was very keen to have a go at the "Hun".

6. The Zimmermann Telegram and the sinking of seven American merchant ships.

7. Britain softly manipulated the USA into joining the war (refer "6"). History can't really blame them.

Amazing that no one here dares to mention the Balfour declaration. It was the primary reason the newspapers & public media of the time were instructed to turn American popular opinion against Germany.

As for the Lusitania, divers that inspected the wreckage in 2008 reported the discovery of around four million rounds of U.S.-manufactured Remington .303 bullets in the Lusitania s hold (they were marked as being "cheese, butter and oysters"...it was not just a passenger ship, it WAS illegally carrying munitions, and the Germans had every right to sink it as an enemy vessel.

Simply put, if the Americans had not been smuggling munitions and war materiel to the allies, the Germans would not have been suggesting to Mexico that Mexicans give the U.S. a separate front to fight on. With the exception of the banking losses that U.S. banks would have experienced, which has already been mentioned here, there was no real reason at all whatsoever for any American soldier to die in this war, we had no dog in this fight.

Proving once again, that all wars are "banker s" wars.

The staggering ignorance of the previous answers is a blemish on our current educational system. Pearl Harbor was WWII.

The US entered WWI pretty much against popular opinion. But what allowed president Wilson to go ahead was unrestricted submarine warfare by the Germans which sunk hundreds of thousands of tonnes of US merchant ships as well as the passenger liner Lusitania.

And some think that the US just was itching to kick some butt.

1) the Zimmerman telegram ( message to Mexico asking them to join the central powers, also promising Texas back. Mexico never got message because British interception. )

2) the sinking of American ships by German U-boats ( submarines )

3) sinking of the Lusitania ( British ship containing Americans on it

the assassination of archduke Francis Ferdinand also known as the spark is also a major reason

The Germans started attacking ships with American citizens on board. Germany also sent a message to Mexico, saying that if Mexico declared war on the USA, Germany would help Mexico regain Texas, New Mexico and California which had been lost during the Mexican-American war. That was called the Zimmerman Telegram.

We're talking WWI here, not WWII. The Germans sank the Luscitania. I'm sure I spelled that wrong. The Germans were not supposed to sink it. It was not a military boat, and 3 Americans died.

Pearl Harbor got the US involved in WWII.

The assassination of Francois Ferdinand, an archduke,and his wife, by Princip Gavrilo, a Serbian nationalist was why the war started. It also started because of the many alliances that were formed before it. When one country declared war, all of it's allies had to too.

Sorry I thought you said WWII, not WWI. Anyway. The assassination of the Archduke of Austria-Hungary Franz Ferdinand set off the powder keg in the Balkans. The U.S. did not join the war until 1917 due to increasing German aggression, which included the sinking of passenger ships and American merchant ships by German U-boats. Woodrow Wilson tried to negotiate terms with Germany but after British blockades of the North Sea which basically cut all U.S. trade to Germany all financial ties were abandoned. The Allies owed millions of dollars of money to the U.S. for the skyrocketing shipments of war goods. We became so financially tied to the Allied countries, especially France and England, that many economists pushed to enter the war. Many Americans felt a duty to protect these countries, for they had been or allies for years.

Zimmerman note Germany asked Mexico for help to attack America and the sinkinking of the submarine

the sinking of the passenger ship was the main reason why we join in WWI

The immediate reason that the United States entered World War II was the the Japanese attacked Pearl Harbor on December 7, 1941. However, President Roosevelt had been looking for a way for the United States to enter the war on the side of the UK and the USSR, and Japan's attack provided a good reason for entering the war.