Japan was on the losing end of World War II, and besides suffering from that defeat which entailed the fiery destruction of much of residential Tokyo, it also suffered through two atomic bombs dropped onto its country by the United States of America. You might think that the above would have created massive resentment within Japan of America, but in actuality, to the credit of the Japanese government and the Japanese people, they accepted their defeat with equanimity, as essentially being defeated by a stronger nation which led to their desire to learn from the best, which Japan aptly accomplished.
There are huge economic advantages to being located in the Far East and subsequently being treated by the greatest economic power in the world as a "favored" nation within that sphere. Additionally, the dismantling of the Japanese military- industrial complex meant that monies, equipment, personnel, and resources that were previously spent in the upkeep of being an imperial power, were now redirected into becoming an economic power, to which, the United States was the partner that helped to provide the necessary resources and capital to jumpstart the Japanese miracle. So too Japan represented an insular society, with little or no internal division, hard working people, intelligent, educated, and determined to do better, with a young work force and the resiliency to perform at a highly competent rate. All of this led to the Japanese economic miracle, to which in the decade of the 1960s Japan averaged GDP growth of a staggering 10% a year, eventually to which this island nation with little natural resources became the second largest economy in the world by 1978. Japan, today, remains very close to America, and would not be the same country if not for its special relationship with America, in conjunction with its dedicated work ethic and consistently high labor productivity rate.
In 2003, America, decided for whatever dubious reasons that Saddam Hussein, President/Dictator of Iraq, must be forcefully removed from office and thereby America with assistance from other coalition forces attacked Iraq and within 45 days, President Bush declared victory by stating, "Mission accomplished". Despite the United States calling their military operation: "Iraqi Freedom", thirteen years after this military invasion, nobody would consider Iraq to be a free state, let alone a successful state, but most would consider it to be a failed state. The GDP per capita (constant LCU) for Iraq in 2002 was $3,716,142, whereas in 2014 it was measured at $4,871,914, and while this is an improvement, it's hardly earth shattering, in fact its rather pedestrian, despite the fact that Iraq's oil production is 50% higher than what it was in 2002, and further to the point that Iraq is one of the largest oil producers in the world.
While there are myriad reasons why Iraq is a failed state, one need not look too far to understand that the artificial borders created out of the Ottoman Empire, created tensions, by virtue of the fact that these borders included within the same nation state factions that historically did not get along well with each other, which in particular were the Sunnis, the Shia, and the Kurds. Any President of any country having to deal with these divisive interests would be hard pressed to have or to bring lasting peace to such a nation, and in this, Saddam Hussein, a Sunni, was no exception. So too, when occupied by the United States of America, Iraq fared no better, degenerating into local battles between different factions with America often caught within the crossfire.
Whether Iraq is ungovernable or not, America now knows that Iraq despite its great natural resource of oil, is no Japan, and never will be, indicating that it is foolish to believe that divisive factions with long standing animosities towards each other will somehow or another, unite under the umbrella of American hegemony.