Imagine for a moment, if you will, feeding every single person in London into a mincer. Because that was what happened in WWI. The combat deaths of the allies alone were equivalent roughly the entire population of our city. That many you could not see all of them in your lifetime. The guns fell silent on the 11th of November, but after Versailles they were only catching their breath.
An extremely good program was shown on BBC, and is still available on the iPlayer The First World War From Above. Watch it to see Ypres and Paschendale in a way you have never seen them before, and remember.