Japan's dependency on the U.S. nuclear umbrella and the bilateral "nuclear bond" have been strengthened through under-the-table discussions, according to a 2009 Japanese government memo recently obtained by Kyodo News and interviews with officials.

The secret memo, written by strategists nine years ago, demonstrates why the administration of Prime Minister Shinzo Abe gave such high marks to U.S. President Donald Trump's Nuclear Posture Review, released in February, which emphasized Washington's commitment to defend its allies, including Japan, in an apparent shift from Obama-era policy.

The memo was presented to the U.S. Congressional Commission on U.S. Strategic Posture, which was composed of 12 nuclear experts and chaired by former Defense Secretary William Perry. A primary purpose of the bipartisan commission was to make concrete proposals to the administration of then-President Barack Obama, which was drafting its own policy review.