Proof is in the pudding, as they say. "It was known that the very wealthy were interested in involving the American government in that war, and Secretary of State William Jennings Bryan was one who made note of this. "As Secretary [Bryan] had anticipated, the large banking interests were deeply interested in the World War because of wide opportunities for large profits. On August 3, 1914, even before the actual clash of arms, the French firm of Rothschild Freres cabled to Morgan and Company in New York suggesting the flotation of a loan of $100,000,000, a substantial part of which was to be left in the United States, to pay for French purchases of American goods."--(source: http://www.threeworldwars.com/world-war-1/ww1.htm).
But also the British and American leaders were scheming to get America into the war via the sinking of the Lusitania ship. "Even though Wilson proclaimed America's neutrality in the European War, in accordance with the prior admonitions of George Washington, his government was secretly plotting to involve the American people by having the Lusitania sunk. This was made public in the book The Intimate Papers of Colonel House, written by a supporter of the Colonel, who recorded a conversation between Colonel House and Sir Edward Grey of England, the Foreign Secretary of England:
Grey: What will America do if the Germans sink an ocean liner with American passengers on board?
House: I believe that a flame of indignation would sweep the United States and that by itself would be sufficient to carry us into the war."
Yes, many powers within the US and abroad worked together to get the US into the war to fill their pockets with money, millions and millions. At the same time the US went into debt to fund the war to end the German attacks on France.
The Zimmerman telegram, an telegram 'intercepted' by British forces sent from Germany to Mexico, was clearly false. One of the major reasons why America got into the war was because of the Zimmerman telegram. Apparently, Germany was scared that America would join the war, so Germany wanted to throw the first hit by having Mexico go to war with America. There are two major flaws with the premise of the idea. One is that Germany clearly didn't want America to enter the war so by having America join the war would be bad regardless of whether or not they tossed the first stone. America was the sleeping giant that Germany didn't want to wake up. Secondly, The idea that Germany would invite Mexico to regain the land they lost 75 YEARS AGO is ridiculous as Mexico would have no reason to attempt to retake such lands that they had lost. Remember after 75 years, these lands speak English and people identify as Americans in an organized voting state. The message is clearly fake and was made up by someone to make America have a reason to join the war. Seeing that Americans were persuaded to join a war through a fake document, yes, America was manipulated to join the war.
The situations surrounding WWI were confusing and, terrifyingly, largely arbitrary in many ways, yet the US entering the war was one of the less disingenuous of entrances. The US came in to the war on the side of the British and French largely because German Uboats attacked US passenger ships.
Manipulation is not the correct term to use when speaking of a country that goes into war no matter which world war is the subject of the question. Manipulation means that there were diplomatic reasons that mandated the war in a forceful manner. War is declared after extensive congress litigation.