The Japanese are a monolithic people, willing to join together to do whatever it takes to ensure the future of Japan, including bowing down to temporary American hegemony. Iraq is made up of at least four separate groups of people (sunni, shia, Kurds, Christians) with four separate agendas, and convincing them to work together would have taken much longer--and it's too late now, thank you Barack Obama.
Like maybe 500 years.