factories' development, the area acquired a reputation as a vicious slum and breeding ground for crime. By 1904, 22 of the 25 housing units in Brownsville were tenement housing; three years later, only one of these 25 housing units was not a tenement. It became as dense as the very densely packed Lower East Side, according to one account. This also led to dangerous conditions; a 1935 collapse of a tenement stairway killed two people and injured 43 others. This overcrowding was despite the availability of empty space in the fringes of Brownsville. There were also no playgrounds in the area, and the only park in the vicinity was Betsy Head Park. In the early 20th century, the vast majority of Brownsville residents were born outside the United States; in 1910, 66% of the population were first-generation immigrants, and 80% of these immigrants were from Russia. By 1920, over 80,000 of the area's 100,000 inhabitants were Russian Jews, and Brownsville had been nicknamed "Little Jerusalem". In the 1930s it was considered the most densely populated district in all of Brooklyn. Brownsville was also considered to have the highest density of Jews of any place in the United States through the 1950s. The population remained heavily Jewish until the middle of the century, and the neighborhood boasted some seventy Orthodox synagogues. Many of these synagogues still exist in Brownsville, albeit as churches. Brownsville was also a place for radical political causes during this time. In 1916, Margaret Sanger set up the first birth control clinic in America on Amboy Street. Throughout the 1920s and 1930s, the neighborhood elected Socialist and American Labor Party candidates to the state assembly. Two Socialist candidates for mayor in 1929 and 1932 both received roughly a quarter of Brownsville residents' mayoral votes. Socialist attitudes prevailed among Brownsville residents until World War II. The area's Jewish population participated heavily in civil rights movements, rallying against such things as poll taxes, Jim Crow laws, and segregation in schools. The area was fairly economically successful in its heyday. In 1942, there were 372 stores, including 8 banks and 43 stores selling menswear, along a stretch of Pitkin Avenue, which employed a combined 1,000 people and generated an estimated $90 million annually (equal to about $ today if adjusted for inflation). The median income of $2,493 in 1933 (about $ today) was twice that of a family living in the