I was looking at voting patterns for this class I had and always wondered why states like Minnesota was largely Republican until JFK in 1960, and why some like the north-eastern states largely Republican until roughly 1988, and why some west coast states largely Republican until 1988. It was something that always bugged me.
I know for the south, it had something to deal with an ideological shift, but was there other reasons why they were mostly democrat until LBJ came?
What you have stumbled upon is called Realignment Theory.
Realignment is when a person or group changes from one political party to another. Not to be confused with De-alignment, switching from a party to no party identification, even if you do still vote for one party consistently.
Since the mid 19th century, and especially after the Civil War, the two political parties had formed mostly solid control over geographic areas. After Reconstruction ended, blacks were again disfranchised, and the strong use of "Bloody Shirt" politics gave the Democratic party a firm hold on the South. Meanwhile, pro-business politics, and liberal race politics (to some extent), were in the Northeast, then spread West as the U.S. populated the coast and the Sunbelt grew post World War 2.
Here is an interesting thing to consider. The South was almost entirely Democratic and only gradually shifted to the GOP (Republican) from 1946-1990. However, the South in the Presidential election was regularly voting for the GOP candidate, but down ballot would mostly vote Democrat.
As to why the South remained Dem. for so long and why it changed, I can answer. Since the end of Reconstruction there were few bastions of GOP politics in the South. This was because of a few big reasons.
The GOP wanted a small party in the South. The Republican party was still competitive in the Presidential election, and won several times before and after FDR. When your party wins the presidency, your party gets the spoils. Your party gets the appointments to top positions, the best jobs, the best contracts, the all coveted Postmaster Generalship. With a smaller party in the South you shrink the pool of fellow Republicans to compete with for spoils/patronage.
Building up a party from the local level takes A LOT of money, time, man hours, and quality candidates. After Reconstruction the largest base of GOP voters, blacks, became disfranchised and with it, most of the party's viability in the deep South. Gradually, the party did rebuild itself, and also had...
Ideological realignment was key to the South and West, or Sunbelt, switching from the Solid Democrat South to the GOP South it is now. From 1932-1990 FDR's New Deal Coalition dominated politics in most cases. Thing is, the Democratic party, the New Deal Coalition as it was referred to, included Liberal Democrats who were for progressive attitudes on race, and Conservative Democrats who were not. The Conservative Democrats being largely in the South. At the same time Civil Rights were being protested for by Martin Luther King and the SCLC, people were moving out West, bringing their Conservative ideologies with them. For every political movement there is a counter movement, but the conservative movement wouldn't be launched into the forefront until Reagan in 1980.
To sum, the New Deal Coalition was such a broad amalgamation ideologies, liberal and conservative, that enjoyed so much success that it took time for people to switch parties. Some people attribute the change entirely to the Civil Rights movement, claiming racist Democrats in the South switched parties in retaliation to their own party passing such measures in Congress. Others point to the fact that people rarely switch party, in fact only a elected officials like Strom Thurmond did switch party, and instead suggest that in was part of the gradual uptick in GOP voting in the South as generations died off and new ones took their place.
This is not every piece of information for any of the theories because that would be entire libraries of information. I would be happy to elaborate as best I can on anything you feel I missed or you want to know more about.