Why is Japan not part of the new AIIB? Why are countries like the United States, France or Germany are against it?
proposed by the government of China
Somehow, I find it unsurprising that China's arch-opponent wasn't playing ball
... regarded by some as a rival for the IMF, the World Bank and the Asian Development Bank (ADB), which are regarded as dominated by developed countries like the United States
Wikipedia article also pretty clearly states the official explanations from Japan and US for why it ain't their club
The United States' officials have expressed concerns about whether the AIIB would have high standards of governance, and whether it would have environmental and social safeguards.
"Japan is dubious about whether (the AIIB) would be properly governed or whether it would damage other creditors"