Underlying this book is the conviction that a sane nationalism, when it understands itself, points the way to internationalism at its completion. The principle that builds the single State cannot end with the single State. This has been felt, sometimes clearly, more often dimly, by all the best thinkers of Europe. The lesson has been hard; indeed, it has never been learnt, but it ought to be learnt and it could be learnt. Gradually the sense of its need has grown and in that growth lies hope. The survey which follows has been, for reasons of space, confined on the whole to Europe, but the same factors are and always have been at work in all nations.