In terms of sheer numbers, the cost of World War I in human life was staggering beyond any war that had preceded it. The number of civilian casualties is unknown but is certainly in the millions. The chart below shows those nations that lost 100,000 men or more (killed, wounded or missing) in combat. Some smaller nations had fewer casualties but a much smaller population; hence, they deployed a smaller military force but suffered a high percentage of casualties. Montenegro, for example, suffered “only” 20,000 casualties—but from a force of 50,000 that reflected a loss of 40%.

Beyond its own battlefield casualties, the War to End War spawned the Russian Civil War, the Balkan Wars and, many would argue, the Second World War. With the end of World War I, the Ottoman Empire was dismantled and national boundaries drawn by Britain and France without regard to ethnicity, religious affiliation, or traditional homelands. The deaths in the Mideast (and worldwide in jihad-inspired terrorist attacks) as a result of those decisions continue to the present day.

Nations listed are color-coded to reflect the year they entered the war and the side on which they fought, the Allied Powers (or Entente) or the Central Powers. Numbers are rounded; sources disagree about actual numbers.