The concept is broader than a military organization, hence “concert” instead of “alliance.” In a subsequent article in The American Interest,[1] they affirm that roughly 60 countries would qualify for membership under these criteria.
Around the same time, following a 2004 exchange with Jean Elshtain on just war theory, John Davenport of Fordham University proposed a "federation of democracies" in a 2005 article.
[6] According to the Princeton Project's final report released on September 27, 2006, this alternative body's purpose would be to strengthen security cooperation among the world’s liberal democracies and to provide a framework in which they can work together to effectively tackle common challenges - ideally within existing regional and global institutions, but if those institutions fail, then independently, functioning as a focal point for efforts to strengthen liberty under law around the world.
[7] On September 16, 2006, Anne Bayefsky at the Hudson Institute, published a nearly identical proposal to establish an organization called the United Democratic Nations in The Jerusalem Post.
This work includes a list of 50 global public goods that cannot be adequately secured by free markets or international networks of NGOs and IGOs, according to the author.