Parrington defined the three phases of U.S. history as Calvinistic pessimism, romantic optimism, and mechanistic pessimism, with democratic idealism as the main driving force. Parrington defended the doctrine of state sovereignty, and sought to disassociate it from the cause of slavery, claiming that the association of those two causes had proven "disastrous to American democracy," removing the last brake on the growth of corporate power in the Gilded Age as the federal government began shielding capitalists from local and state regulation. For two decades "Main Currents in American Thought" was one of the most influential books for American historians. Reising (1989) shows the book dominated literary and cultural criticism from 1927 through the early 1950s. Crowe (1977) calls it "the "Summa Theologica of Progressive history." Progressive history was a set of related assumptions and attitudes, which inspired the first great flowering of professional American scholarship in history. These historians saw economic and geographical forces as primary, and saw ideas as merely instruments. They regarded many dominant concepts and interpretations as masks for deeper realities. Reinitz (1977) stresses Parrington's heavy use of historical irony, which occurs when the consequences of an action emerge contrary to the original intentions of the actors. Parrington represented the Progressive School of historians which stressed the duality of good versus evil in the American past. Yet, in his final volume of "Main Currents" he concluded that the Jeffersonian farmer, the Progressives' traditional democratic hero, had joined forces with the greedy business community to produce a destructive form of capitalism which culminated in the 1920s. His progressive interpretation of American history was highly influential in the 1920s and 1930s and helped define modern liberalism in the United States. After receiving overwhelming praise and exerting enormous influence among intellectuals in the 1930s and 1940s, Parrington's ideas fell out of fashion before 1950. Richard Hofstadter says "the most striking thing about the reputation of V L Parrington, as we think of it today, is its abrupt decline...during the 1940s Parrington rather quickly cease to have a compelling interest for students of American literature, and in time historians too began to desert him." Hofstadter shows how Parrington's ideas came under heavy assault in the 1940s and 1950s, naming Lionel Trilling as especially influential in the attack. Harold Bloom says: "Parrington was, in turn, condemned to obscurity by critics like Lionel Trilling, who sharply criticized his literary nationalism and his insistence that literature should appeal to a popular constituency."