Mexico making a bid for global supremacy? Poland becoming America's closest ally? World War III taking place in space? It might sound fantastic but all these things can happen. In ''The Next 100 Years'', George Friedman, author of the huge bestseller ''America's Secret War'' offers a lucid, highly readable forecast of the changes we can expect around the world during the 21st century. He predicts where and why future wars will erupt, and how they will be fought; which nations will gain and lose economic and political power; and how new technologies and cultural trends will alter the way we live in the new century.