LBJ fought all civil rights bills the Republican put up in the late 50'.Quote from epiktetos:
History is better in text form.
http://en.wikipedia.org/wiki/Southern_strategy
As the South became more prosperous it began to vote more Republican.
LBJ saw this trend, that the Dems were going to lose the south eventually.
LBJ flip flopped and moved to give the Republicans the additional Democratic votes need to pass the 1965 bill.
LBJ knew he could lock in the rest of the Black vote ,and he did .Blacks went from 40% to 95% vote to democrats.
The fundamental change was the Dems changing their policy on segregation.
The so called Southern Strategy was happening anyways. It was the Black vote strategy that was the forced event