<P> The American entry into World War I came in April 1917, after more than two and a half years of efforts by President Woodrow Wilson to keep the United States out of the war . Apart from an Anglophile element urging early support for the British, American public opinion reflected that of the president: the sentiment for neutrality was particularly strong among Irish Americans, German Americans, and Scandinavian Americans, as well as among church leaders and among women in general . On the other hand, even before World War I had broken out, American opinion had been more negative toward Germany than towards any other country in Europe . Over time, especially after reports of atrocities in Belgium in 1914 and following the sinking of the passenger liner RMS Lusitania in 1915, the American citizens increasingly came to see Germany as the aggressor in Europe . </P> <P> As U.S. president, it was Wilson who made the key policy decisions over foreign affairs: while the country was at peace, the domestic economy ran on a laissez - faire basis, with American banks making huge loans to Britain and France--funds that were in large part used to buy munitions, raw materials, and food from across the Atlantic . Until 1917, Wilson made minimal preparations for a land war and kept the United States Army on a small peacetime footing, despite increasing demands for enhanced preparedness . He did however expand the United States Navy . </P> <P> In 1917, with Russia experiencing political upheaval following widespread disillusionment there over the war, and with Britain and France low on credit, Germany appeared to have the upper hand in Europe, while Germany's ally, the Ottoman Empire, clung stubbornly to its possessions in the Middle East . In the same year, Germany decided to resume unrestricted submarine warfare against any vessel approaching British waters; this attempt to starve Britain into surrender was balanced against the knowledge that it would almost certainly bring the United States into the war . Germany also made a secret offer to help Mexico regain territories lost in the Mexican--American War in an encoded telegram known as the Zimmermann Telegram, which was intercepted by British Intelligence . Publication of that communique outraged Americans just as German U-boats started sinking American merchant ships in the North Atlantic . Wilson then asked Congress for "a war to end all wars" that would "make the world safe for democracy", and Congress voted to declare war on Germany on April 6, 1917 . </P> <P> On December 7, 1917, the U.S. declared war on Austria - Hungary . </P>

Which weapon was a primary cause of the u.s. entry into world war i