The precipitating event was the integration of the military by Harry Truman in 1947. Strom only carried 4 states and it wasn’t enough to change the result of the 1948 election, but it set the groundwork for the post Voting Rights Act split by southern Democrats, again with Strom taking the lead and culminating with Nixon’s victory in 1968.
It is intellectually dishonest to try to divorce the Dixiecrats and later flip of the south from the democrats to the republicans from the race question. It is what it is, whether one thinks that is a good thing or a bad thing.
Remember that the famous ‘progressive’ President Woodrow Wilson segregated the White House, Treasury Dept and Navy, which was heavily integrated after the Civil War and up to the Wilson administration. His administration actively pushed segregation, followed closely by the KKK marches and conventions in Washington DC.