Peter Turchin theorized that a major driver of the American Civil War was economic. Using his metrics for civil conflict, he identified elite overproduction and popular immiseration as forces that fueled the sectionalism that led to war. Between 1820 and 1860, average wages relative to higher incomes fell by more than 40 percent, while the expansion of the planter class threatened yeoman farmers. The rise of the Free Soil Party, Know-Nothing movement, and later the Republican Party reflected a distressed political environment. Recurrent financial crises, such as the Panic of 1837, severe state debt crises in the 1840s, and Panic of 1857, added further accelerants. The destruction of the Southern planter elite allowed Northern industrialists and political machines to consolidate control over the economy during the Reconstruction Era and to establish a virtual monopoly on the American economy and political system through the Gilded Age.