The United States was never an isolationist country except in a Pickwickian sense of the term. It went through no period of excluding the outside world, as the Japanese did for two hundred years. On the contrary, the United States, in consequence of its openness to immigration, linked itself, between 1790 and 1920, ever more closely by ties of culture and blood to the various countries of Europe. It engaged in trade with them, allowed and invited their economic support in the task of settling and exploiting the American continent, and sent its upper-class children and its best writers, artists, and scientists on mandatory tours of Europe for the good of their souls. Culturally, ethnically, in its historical affinities, the United States has been perhaps the least isolated of nations.