What was the only significant positive union gain prior to the Great Depression in 1929?

The Immigration Act of 1924 was significant in shaping labor dynamics in the United States, but it wasn't a union gain. Instead, the act aimed to limit immigration, particularly from Southern and Eastern Europe, which influenced labor markets by restricting the supply of immigrant workers who were often willing to work for lower wages. This shift inadvertently supported labor unions, as a reduced labor pool allowed unions to negotiate better conditions and wages for domestic workers.

In contrast, the Haymarket Riot of 1886 and the Pullman Strike of 1894 were pivotal events demonstrating the growing tension between labor organizations and the government or employers. While they raised awareness about labor rights, they did not yield significant immediate positive gains for unions.

The Sherman Act of 1890 is important as it was primarily anti-trust legislation rather than pro-labor. It aimed to curtail monopolies and protect trade, creating an environment where courts were often hostile toward unions under the notion that they restricted trade.

Understanding this context highlights that the focus of positive union achievements must reflect significant legislative or socio-economic gains directly benefiting labor rights, rather than measures that merely shaped the environment in which unions operated.