Keynes provides a footnote to this paragraph:
"Only after the most painful consideration have I written these words. The almost complete absence of protest from the leading Statesmen of England makes one feel that one must have made some mistake. But I believe that I know all the facts, and I can discover no such mistake."
The reference is to the wide gulf between the broad outline of terms in the armistice (commemorated today), and the treaty negotiations which were supposed to specify the details of that armistice, but instead instituted a new (and as Keynes put it) "Carthaginian peace". The culprits for Keynes were a vengeful Georges Clemenceau, a politically opportunistic Lloyd George, and a naive, lackluster Woodrow Wilson who probably wanted what Keynes wanted but was completely in over his head in Paris. We often hear about how Keynes clobbered Wilson in the book, but actually the treatment of Lloyd George is much, much worse (and perhaps he deserves every bit of it).