Like I said, this is where I can tell you really aren't as old as you claim to be.
The Democrats ONLY dominated elections because of the black vote in that time period. Before 1932, it was a regional party in the south. It's a lot more complicated, such as the growing strength of Unions in the North, and the decline of big city Republican political machines.
First, Democrats continued to dominate congressional elections until the 1990's. So we are only really talking about the Presidency.
So, from 1968 to 2024, (56 years) Republicans held that office for only 32 years. Democrats have held it for 24. And it would be more if we weren't still using a 17th century anachronism to select presidents.
Now, I do admit that Republicans have used racism to get stupid white people to vote against their own economic interests but as whites continue to decline as a share of the population, that's going to be an increasingly less useful tactic.