Explaining proliferation: why interest groups are common in the United States Many kinds of cleavage in the country Constitution makes for many access points Public laws factor the non profit sector Political parties are weak The birth of interest groups Periods of rapid growth Since 1960, 70 percent have established an office in Washington, D.C. 1770s, independence groups 1830s and 1840s, religious, antislavery groups 1860s, craft unions 1880s and 1890s, business associations 1900s and 1910, most major lobbies of today Factors explaining the rise of interest groups Broad economic developments create new interests Farmers produce cash crops Mass production industries begin Government policy itself Created veterans' groups--wars Encouraged formation of Farm Bureau