Post-WWI bitterness refers to the widespread resentment and disillusionment experienced by many nations and populations following the end of World War I in 1918. This feeling was particularly strong in countries like Germany and Italy, where the harsh terms of the Treaty of Versailles and other peace settlements led to economic hardship, national humiliation, and a sense of betrayal. These sentiments contributed significantly to the rise of extremist political movements, including fascism and totalitarianism, as people sought strong leadership to restore national pride and stability.