Twenty-seven countries on five continents were involved in World War I. This war was also called the Great War or The War to End All Wars. was the bloodiest and most costly of all the previous wars. The total casualties numbered thirteen million with another thirteen million wounded. The cost of this war was estimated to be more than $337 billion (Young World Book 364). World War I was different from previous wars because of the new types of weapons and methods used on the battlefields, in the skies, and on the seas. New weapons and new m ....