 The Allied Powers in World War I (also known as the Entente Powers) were initially the United Kingdom, France, the Russian Empire, Belgium, Serbia, Montenegro and Japan, joined later by Italy, Portugal, Romania, the United States, Greece and Brazil.Some, such as the Russian Empire, withdrew from the war before the armistice due to revolution or defeat.After the end of World War II and during the Cold War, the North Atlantic Treaty Organization (NATO) was formed as a political and military alliance that promotes democratic values.