Final answer:
Jacob Riis claimed that in the chief city of America, a distinctly American community could not be found because New York City was a mosaic of diverse ethnic enclaves rather than a homogenous American identity. His work, including documentation and photography, exposed the severe urban poor living conditions and spurred changes in tenement laws.
Step-by-step explanation:
Jacob Riis, a social reformer and pioneering photojournalist, depicted the harsh realities of life in New York City's tenements in the late 19th century. In his famous work, How the Other Half Lives, Riis exposed the deplorable living conditions of the urban poor to the American public. His statement that 'the one thing you shall vainly ask for in the chief city of America is a distinctly American community' reflects his observation that, despite America's ethos of economic opportunity and upwards mobility, New York City at that time was comprised of many diverse ethnic enclaves with significant economic disparities, making it difficult to find a homogenous American identity or community.
By bringing these conditions to light through both shocking narratives and photography, Riis hoped to generate public support for change and advocate for tenement reform. His work was instrumental in the passage of tenement laws and gave visual urgency to the plight of the poor, challenging the notion of American Exceptionalism in the face of evident poverty and dire living conditions.