OK first a historical background
After the rise of 1800s imperialism Muslims realized that Islamic powers really didn't have Allah on their side and in general the west was unbeatable even by the ottoman caliphate.
This gave rise to a reformist movement that adopted salafism
The idea that the Islamic world degenerated the last 1000 years and Muslims should denounce traditionalist baggage and return to the salaf aka the first three generations of Muslims
The early salsfist reformers had little to do with modern day ones, and in general were the inventors of modern day Islamic apologetics.
Many supported for example anti imperialist co-operation with non Muslims in inidia and Mena, and that you should criticize old Islamic structures of government (although your criticism should be based on the Quran and hadith)
In Shia Iran this movement was associated with red shiism a movement that despite leading the Iranian revolution was betrayed by the mullahs.
In Egypt the movement gave birth to the Muslim brotherhood and wahabism in Saudi Arabia.
So what changed
In general the salsfist hope to spread true Islamic education and that quickly clashed with all modernizing attempts
Also there was a split between salsfists focused on peaceful education and others on violent jihad.
With the spread of communism and the Iranian revolution many monarchist governments were afraid of popular revolts thus the started funding imams inside and outside their states, thus connecting Islam with loyalty to the king.
Since most of this kingdom were mostly sunni they focused on sunni salafism.
The Shia minority outside Iran had an clear interest in pushing for liberal tolerance since any Islamist movement will be majority sunni
Class wise is as tribalistic as sunni extremism in my experience
A Shia imam will support the axis of resistance a sunni the wahabists