Which event marked a pivotal shift in U.S. civil rights history in the 1960s?

The Selma to Montgomery marches are indeed a significant event in U.S. civil rights history during the 1960s. This series of protests focused on voting rights for African Americans and highlighted the widespread racial discrimination present in the South. The marches, which took place in 1965, drew national attention to the struggle for civil rights and resulted in a greater public awareness of the injustices faced by African Americans.

The events in Selma directly led to the passing of the Voting Rights Act of 1965, which aimed to eliminate barriers to voting for African Americans. The dramatic imagery of the marchers being confronted by law enforcement, particularly during a brutal confrontation known as "Bloody Sunday," galvanized support for the civil rights movement across the nation.

In contrast, while the Civil Rights Act of 1964 is also a landmark piece of legislation that solidified many legal protections against discrimination, it was the marches that acted as a catalyst for further legislative action regarding voting rights. The other options, including the Boston Tea Party and the Emancipation Proclamation, do not specifically pertain to civil rights struggles of the 1960s; instead, they represent earlier historical events in U.S. history with different focuses.