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If you look at what Colin Powell said in Washington Post editor Karen DeYoung's biographical book about him. She had said that Colin Powell had conveyed to her that the "JINSA crowd," the Jewish Institute for National Security Affairs, which Dick Cheney is associated with, is control of the Pentagon and pushed us into Iraq and now is doing similar to get us to attack Iran.
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"Sniegoski leaves no stone unturned in exposing the Israeli-neocon alliance and its catastrophic consequences in the Middle East." - Jonathan Cook
"JINSA is the Jewish Institute for National Security Affairs, a hawkish think tank that supported the Iraq war. Thomas Neumann, Jinsa’s executive director, said he was not offended by Powell’s reference, although he was surprised that the former secretary of state would single out a Jewish group when naming those who supported the war. 'I am not accusing Powell of anything, but these are words that the antisemites will use in the future,' Neumann said." - The Jewish Daily Forward, Groups Fear Public Backlash Over Iran
As for a motive why top neocons would want to deceive the American people into a war with Iraq, you can read about "A Clean Break: A New Strategy for Securing the Realm" which reveals that attacking Iraq was an agenda long before the 9/11 attacks which they dishonestly try to use as an excuse for the Iraq war. Three of Bush's top national security advisors had worked for "conservative pro-Israel think tanks" creating a plan in violation of international law which the necons do not respect. James Bamford, in his book A Pretext for War, writes, 
"the blueprint for the new Bush policy had actually been drawn up five years earlier by three of his top national security advisors. Soon to be appointed to senior administration positions, they were Richard Perle, Douglas Feith, and David Wurmser. Ironically the plan was originally intended not for Bush but for another world leader, Israeli Prime Minister Benjamin Netanyahu. At the time, the three officials were out of government and working for conservative pro-Israel think tanks. Perle and Feith had previously served in high level Pentagon positions during the presidency of Ronald Reagan. In a very unusual move, the former--and future--senior American officials were acting as a sort of American privy council to the new Israeli Prime Minister." 
"The Office of Special Plans (OSP) was directed to find evidence that could be used to sell the war against Iraq. It was headed by Adam Shulsky, a neoconservative long associated with Wolfowitz, and its ranks included several recruits from pro-Israel think tanks like Michael Rubin from the American Enterprise Institute, David Schenker from the Washington Institute for Near East Policy, and Michael Makovsky, who had worked for then Prime Minister Shimon Peres after graduating from college." p251, The Israel Lobby and U.S. Foreign Policy, by John J. Mearsheimer and Stephen M. Walt
