US foreign policy has been studied with the instrument of the models, that represent how a diplomacy of the main contemporary (conservative, liberal, neo-conservative or leftist) Western political cultures would work at the analytic level. Then, the empirical analysis aims at comparing those models with the historical evolution of the US diplomacy. In the Cold War, conservatism has been almost always applied in the US diplomacy, with few exceptions (the Vietnam’s war). In the 1990s (with Bush and Clinton), conservatism remained the prevailing diplomatic political culture, even if liberal and leftist foreign policies were also applied: for example in Bosnia's and Kosovo's wars. After 2001 (with Bush Jr.), the neo-conservative hybrid emerged in the Iraq’s war, but then was abandoned. Since 2009, conservatism is no longer the prevailing political culture in the US diplomacy, as the diplomacy of the "lesser evil" was abandoned in the Arab spring and in the Libyan war. Obama and Trump have not been able to implement coherent diplomacies aiming at promoting either interests or values. Obama has been volatile at first, then has tried to implement a leftist diplomacy, but he has not been fully coherent; at the end, Obama was uncertain and passive. Trump is more (even if not fully) coherent, and he is assertive and reluctant at the same time; Trump is applying a “soft” conservative diplomacy, abandoning the world order ideas of the 1990s. However, the empirical evidence shows that the USA have not been a great power anymore: neither with Obama, nor with Trump.
