Changes in warfare (by creation, extension, or reduction):
-the use of barbed wire, poison gas, and flame-throwers
-trench warfare (not new but extended in length and duration; defense was more probable, given the difficulty of offense and the use of machine guns for defense)
-the importance of cavalry (this is a recurring theme in the book-- that the Brits and French kept expecting that the cavalry would eventually play a pivotal role, as it had in the past)
-the use of (highly effective) machine guns (the Brits had used them in their African "wars" to great effect)
-the use of colorful uniforms
-the origin of tanks (although highly ineffective until the end of the war)
Cause and effect:
-led to World War II
-dramatically reduced the power of the British Empire
-triggered the Russian Revolution and a bloody civil war (this concerned the European governments which feared the same sort of uprising, especially given the pain of the War)
-sped up the women's suffrage movement
-led to the Great Influenza of 1918 where about 50 million died, starting at an army base in Kansas and brought to Europe by American soldiers (If you include the Flu deaths, WWI was more deadly-- in absolute numbers and especially in terms of percentages than WWII.)
Some amazing stats:
-700 million rounds of artillery and mortar
-the front-line trenches ran for 475 miles
-German U-boats sank more than 5,000 merchant ships
-8.5 million men killed; 21 million wounded
-35% of German men between 19-22 years old were killed
-50% of all French men between 20-32 were killed
-Britain lost 722K men; France lost 1.4 million; Russia lost 1.5 million; Germany lost more than 2 million
-civilian war deaths are estimated at about 20 million, including the Turkish genocide of the Armenians and the Russian Revolution
-the Brits lost 57,000 men on July 1, 1916 during "the Somme offensive" (almost half of the troops there) and another 30,000 on a single day in September
-the French lost 300K troops in a one-month period
-in a six-month period, the Russians lost 1.4 million men
-20,000 men refused the draft in Britain (the peace movement is a key part of the book)
Some other interesting factoids:
-Until 1871, British officers had to purchase their commissions.
-Compared to soldiers, a significantly higher proportion of officers were killed.
-Coming into WWI, the leaders of Britain, Germany and Russia were kin.
-German leaders estimated that they would defeat Belgium and France in 42 days. (From there, they planned to turn on the "real enemy": Russia.) But the Belgians blew up bridges and roads, slowing down the Germans, giving the French more time to prepare, and giving the Brits more time to jump in.
-The Germans got within 23 miles of Paris in Sept 1914, but couldn't close the gap further.
-The Germans sent only 500K troops to face Russia at the beginning of the war. Vastly outnumbered, they were still largely successful because the Russian army was so inept.
-The "Christmas Truce" (a one-day event that was replicated often afterwards): both sides left their trenches and engaged in not simply a lack of conflict, but pleasant interactions. This is a terrific "game theory" example.
-During the War, the Brits traded rubber to the Germans for precision optics through Switzerland.
Hochschild provides context to explain how the assassination of Archduke Ferdinand and his wife set off the War. The Austro-Hungarians were "looking for any possible excuse to invade, dismantle and partition Serbia." Other contributing factors: the strength of rival alliances made the threat of war more prominent; the long time required for mobilization made steady preparation more important; and the advantage of attacking first (and the perception of the problems stemming from being attacked first). At least to an economist, it's interesting that game theory and imperfect information play such a key role here.
And finally, although it's difficult to summarize succinctly, Hochschild spends much ink on the Peace Movement, the War Propaganda, and key players-- the most famous of which were Rudyard Kipling (pro-war) and Bertrand Russell (anti-war).