[2] Calleo claimed that there were many similarities between Imperial Germany and the United States, as both were late-comer powers characterized by huge economic growth and a certain arrogance caused by their success.
Calleo has consistently argued that Europe will turn protectionist in the face of China and other countries in order to preserve the national welfare state.
A theorist of the decline of American power, Calleo sees Europe as an ally to the US but also as a friendly counterweight.
From 2011 he also acted as Advisor to Fair Observer, an online magazine covering global issues from a plurality of perspectives, on editorial issues with a focus on Europe and the U.S.[3] David Calleo was married to Avis T. Bohlen, former ambassador and arms control expert.
Calleo owned a former farm house on the Italian island of Elba, where he spent his summers researching and hosting friends.