World War I has often been portrayed as the first modern war of the 20th century. In terms of its nature and its conduct, it was very different from any previous war, and the changes it brought to international politics and economics were profound.
World War I was primarily concerned with the struggle for mastery in Europe, but it was a global conflict that reached across five oceans and three continents. Although it began in the Balkans, the main theaters of war took place in Western and Eastern Europe. It was a struggle chiefly between the powers of central Europe and the rest of the world. It was a conflict in which the greatest of the European powers—Germany—found itself checked and unable to secure victory. The initial German plan to defeat France by means of an outflanking march through Belgium ultimately miscarried. Over the next three years, the Western Front was to see the most obvious development of "trench warfare" and "trench-lock."