books.google.com - International frontiers and boundaries separate land, rivers and lakes subject to different sovereignties. Frontiers are "zones" of varying widths and they were common many centuries ago. By 1900 frontiers had almost disappeared and had been replaced by boundaries that are lines. The divisive nature...http://books.google.com/books/about/International_frontiers_and_boundaries.html?id=r4FJXXciuhsC&utm_source=gb-gplus-shareInternational frontiers and boundaries
