What issue in the 1960s caused a major majority of Southern votes to switch from supporting the Democratic party to supporting the Republican Party

The issue that caused a major shift in support from the Democratic Party to the Republican Party in the 1960s was the Civil Rights Movement and its associated policies. This was primarily due to the Democratic Party's support for civil rights legislation, which aimed to end segregation and discrimination against African Americans. The Democratic Party, under President Lyndon B. Johnson, pushed for significant civil rights reforms, including the Civil Rights Act of 1964 and the Voting Rights Act of 1965.

These policies, while widely supported by Northern Democrats, were met with strong opposition from many Southern Democrats who held deeply entrenched racist views and relied on segregationist policies to maintain their power. Southern Democrats, known as Dixiecrats, actively opposed civil rights legislation and resisted its implementation.

In response, some Southern Democrats began to defect from the party, feeling betrayed by the Democratic Party's support for the rights of African Americans and desegregation. Many white Southern voters who had traditionally supported the Democratic Party switched their allegiance to the Republican Party, which took a more conservative stance on civil rights. Prominent Southern politicians like Strom Thurmond and Jesse Helms denounced the Democratic Party and became Republicans, with Thurmond even running as a third-party candidate for president in 1948 on a segregationist platform.

The shift eventually solidified in the 1980s and 1990s when the Republican Party appealed to conservative values, including opposition to civil rights policies and a focus on states' rights. This realignment resulted in a significant majority of Southern white voters becoming solid supporters of the Republican Party, a trend that continues to the present day.