The causes of the US entry into WW1 included the Sinking of the passenger ship the Lusitania which was sunk by a German U-Boat. German U-boats then sank six American merchant ships including the Housatonic without warning.

The Zimmermann telegram was then intercepted promising the Mexican Government that Germany would help Mexico recover the territory it had ceded to the United States of America following the Mexican-American War. Wilson asked Congress to declare war against Germany, and the US entry into WW1 began on April 6, 1917.

President Woodrow Wilson and the US entry into WW1 for kids
At the outbreak of World War 1 on July 28, 1914 President Woodrow Wilson adopted a neutral stance in an effort to keep the United States of America from being drawn into a foreign war that was being waged in Europe - refer to the map and the Outbreak and Causes of WW1 in Europe.

Woodrow Wilson Re-elected
On November 7, 1916 Woodrow Wilson was re-elected on an anti-war platform. Most of the European countries believed that the war would be over in less than a year. However, the war continued to rage and it became increasingly difficult for America to maintain its impartial policy of neutrality.

US entry into WW1: US declares War on Germany
On April 2, 1917 President Woodrow Wilson appeared before a special session of Congress on to ask for a declaration of war against Germany. The Senate passed the resolution on April 4, 1917 by a vote of 82 to 6. The House concurred 373 to 50 on April 6, 1917 and President Wilson signed the resolution. The United States of America was at war.

Date of US entry into WW1: April 6 1917
The date of US entry into WW1 was April 6, 1917 when the nation was drawn into World War 1 on the side of the Allies.  The United States of America entered the conflict, two and a half years after the war had begun on July 28, 1914, and declared war on Germany on April 6, 1917.

Facts about American Entry into WW1
The following fact sheet contains interesting facts and information on American Entry into WW1.

On May 7, 1915 the British ocean passenger liner, the Lusitania was sunk by a German U-Boat (submarine). A total of 1,198 people of the 1,959 on board were killed, of which 148 were Americans. There were only 761 survivors

Pro-British propaganda in the press with the invasion of neutral Belgium by Germany,  allegations of atrocities, and submarine warfare encouraged pro-war sentiments and lessened isolationist sentiments.

The American economy was booming. Submarine warfare threatened to stop American trade and brought the threat of another recession in the US.

American banks had made massive loans to the British and the Allies at great profit. American finance and US economic stability was closely tied to the interest of a British victory in the war against Germany to ensure the US was reimbursed.

The Black Tom Explosion was caused by German saboteurs in New York Harbor on July 30, 1916 to prevent British receipt of munitions from the US.

At the beginning of 1917 Germany launched all-out submarine warfare on every commercial ship headed towards Britain and started sinking American ships in the North Atlantic.

On February 3, 1917  German U-boat sank the U.S. cargo ship Housatonic and the United States broke off diplomatic relations with Germany.

Between February 3, 1917 and March 21, 1917 German U-boats sank six American merchant ships without warning

On March 1, 1917 the Zimmermann telegram was published in the American press and inflamed American public opinion against Germany and helped convince Congress to declare war against Germany.

On April 2 President Woodrow Wilson asked Congress to declare war against Germany.  On April 4 the Senate passed the resolution by a vote of 82 to 6 and the House of Representatives concurred 373 to 50

On  April 6, 1917 President Woodrow Wilson signed the resolution., declared war on Germany and fought with the allies in WW1 during which 126,000 Americans died and 234,000 Americans were wounded. WW1 ended on 11 November 1918.

Who supported the US entry into WW1?
The US entry into WW1 was supported by Woodrow Wilson and other powerful political leaders such as Theodore Roosevelt.

Who opposed the US entry into WW1?
The US entry into WW1 was opposed by pacifists, intellectuals and isolationists and various ant-war factions. The pacifists included Quaker and Protestant religious groups and various women's movements led by Montana congresswoman Jeannette Rankin. Pre-war efforts to modernize and enlarge the army were blocked by Congressman James Hay, Democrat of Virginia was the powerful chairman of the House Committee on Military Affairs. Western Progressives (reformers in Western states) who opposed the US entry into WW1 included politicians Robert La Follette, George Norris, William Borah, and Hiram Johnson. Anti-war Socialists like Eugene V. Debs, Union leader and Socialist candidate for President also spoke against American entry into the war.

The Attitude of Americans before US entry into WW1 for kids
The attitude of Americans towards the war varied considerably before the US entry into WW1 as detailed in the following fact sheet:

The war involved the continent of Europe - 3000 miles away from the United States of America. Many Americans wanted to keep their country out of what was perceived as a European War.

Many Americans respected and supported the anti-war views and the neutral stance and of their leader and government who wanted to maintain the prosperity and stability of the nation. Woodrow Wilson quote "We must be impartial in thought as well as in action".

Americans took sides. The majority of American citizens had been born in Europe or were of European descent. Americans sympathized with their 'mother countries'.

Most 'Old Immigrants' from Western Europe supported the Allies valuing the language, heritage and political ideals they shared with Britain. Others valued the links with France which dated back to the support of France during the American War of Independence.

Immigration to America from Europe had exploded during the late 1800's due to the Industrial revolution. The 'New Immigrants' from the eastern European countries  supported their homeland countries.

The nation’s 8 million migrants from Germany supported the Central Powers.

The nation’s 4.5 million Irish-Americans, also sympathized with the Central Powers due to their long standing antagonism towards Britain and the British rule.

The start of the war in Europe coincided with the end of the 1913–1914 Recession in America. The European war resulted in an increased demand abroad for weapons, armaments and the tools of war which began a period of heightened productivity and increased profits, especially in the steel industry.

Leaders of the woman's movement and most religious groups tended towards pacifism

On May 7, 1915 the British ocean liner the Lusitania, which had many American passengers aboard, was sunk by a German U-Boat outraged the American people. Germany made the 'Sussex Pledge' to America (not to sink merchant ships without due warning)

Following the outbreak of World War the 'Preparedness Movement' was a campaign led by Theodore Roosevelt and General Leonard Wood to prepare for war and strengthen the military of the United States. Their aim was also to convince the nation of the need for American involvement in the conflict.

The National Security League, the American Defense Society, the League to Enforce Peace and American Rights Committee supported the Preparedness Movement. Acts of Sabotage such as the Black Tom Explosion strengthened their cause.

The National Defense Act was passed on June 3, 1916 in response to the Preparedness Movement which expanded the size and scope of the National Guard and established the Reserve Officer Training Corps (ROTC) to train and prepare high school and college students for Army service.

The Naval Act of 1916, a massive naval appropriations bill,  was passed authorizing 10 battleships, 10 Omaha-class scout cruisers, 6 Lexington-class battle cruisers, 50 Wickes-class destroyers and numerous other smaller warships to be built over a period of just 3 years.

In early 1917 Germany began to attack American ships in the North Atlantic. The sinking of U.S. cargo ship the Housatonic led America to break off diplomatic relations with Germany.

On March 1, 1917 the Zimmermann Telegram was published in American press and inflamed American public opinion against Germany and helped convince Congress to declare war against Germany. For additional facts refer to 1910 Mexican revolution

On  April 6, 1917 President Wilson declared war on Germany, two and a half years after the war had begun. America fought with the allies in WW1 until the war ended on 11 November 1918.