It depends on how one defines greatest. Certainly the US dominates the world in a manner no other nation has ever done, and it has achieved much in the way of scientific, cultural, and economic development. For awhile the US probably offered opportunities to its citizens that were not available anywhere else. Currently, however, many nations of the world have caught up and even surpassed the US in many areas. In terms of social and political equality the US now lags behind many of the nations of Western Europe, and economically it is in danger of being overtaken by China. This is not to say that the US is still not a wonderful place to live and visit, it means only that there are many things the US could do to make it as great a nation as many Americans proclaim it to be. Under Obama it has taken a hesitant first step in the reform of its health care system; it now needs to reform itself politically and economically in order to catch up to nations that once used to trail it.