Here is a quote from it and I hope it will convince you to look it up and read it (it may be behind a paywall):
Americans and Britons have forgotten this sordid story. Poles have not. Without knowing this history, Westerners will never understand how Poles ... For Poland, World War II did not end in 1945 with a parade and a Paris kiss, but in the ruins of Warsaw ruled over by hostile conquerors who had stood by as the city burned. Poles can perhaps be forgiven for failing to share today’s Western predilections—born of decades of peace and prosperity taken for granted—for postcolonial guilt and ennui, or the fashionable denigration of the nation-state.
Mr. McMeekin's book on World War II, due out in 2020, is tentatively titled “Stalin’s War.”