More recently the US has more accurately been viewed as a militarist 'empire' that fights destructive wars and intervenes in a variety of societies, especially in the Middle East to retain control over oil reserves, and lends crucial support to Israel that not only oppresses the Palestinian people but threatens to convert the entire region into a war zone.
There was a deliberate decision after the failure of the League of Nations to make the next attempt to establish a global political actor sensitive to geopolitical realities. The underlying idea was to provide major states, defined in 1945 by reference to the winners in the Second World War (now an anachronism), with assurance that they could take part in the UN without jeopardising their national interests. In this regard, the UN has succeeded, as none of the big countries has withdrawn, and the Organisation has managed to achieve virtually universal membership of all sovereign states.
If Trump were to go ahead with a renewed policy of hostility toward Iran, it would immediately raise tensions, and could quickly escalate in the direction of war, with grave dangers of producing another Syrian tragedy of massive displacement and prolonged strife that could cause turmoil and disruptions throughout the entire region, and give rise to a new cycle of extremism.
Doing something, however pathetic, is psychologically better than doing nothing. In the current political environment - that is, with no more Cold War tensions - the tendency is to counteract the feelings of fear and vulnerability with a variety of military, paramilitary and police measures, despite the reality that this kind of excessive reliance on force in many ways intensifies the very problem it is purporting to solve.
Trump will have to take up juggling if he goes ahead and scraps the agreement with Iran and at the same time, seeks to avoid alienating Russia, and quite possibly France and Germany. These European countries are already nervous about what the Trump presidency means with respect to the future of the post-World War II international order that has essentially kept the peace on the continent since 1945. This order is far from perfect, of course, and under pressure from other sources, especially due to the rise of chauvinism and European Trumpism.
After the Second World War, facilitating the establishment of the UN and aiding the reconstruction of Europe, the United States was widely viewed, at least in the West, as a benevolent hegemon. In the non-West, the US was often perceived as a supporter of the colonial powers in their struggle to maintain control over their colonial possessions, and was viewed far more critically, especially by emerging elites that were more inclined to socialist development paradigms than to the capitalist ethos favoured by Washington.
As matters now stand, the veto seems inappropriate, given the absence of any deep ideological split between major states, and definitely constrains the war-prevention mission of the UN. Similarly, the present permanent five are out of touch with geopolitical realities, and constitute a remnant of a West-centric world order, casting a shadow of illegitimacy across the activities of the most important organ of global policymaking in the UN System.