Life and social system in Arabia almost remained unchanged from the time of Muhammad to the beginning of twentieth century. Being a harsh desert land with sparse population of mostly nomadic Bedouins and a few settlements of Arabs with very little natural resources, Arabia was residing in inertia of rest from 7th century AD. For the same reasons, Arabia did not attract outside aggressors also.
Expansion of Islamic empire from Arabia to all directions till middle age could not change the life and social system of common Arabs much who in turn, made Islam unchangeable and static in the process.
When Caliphate shifted to Turkey, common Arabs became more comfortable with Qur'an and Hadith. Their Islam grew in consonance with the strong male dominated desert lifestyle of Arabs. Raid on other Arab tribes or caravans was accepted as normal in the society. Slavery, polygamy, frequent and unpredictable change of loyalty and even deceiving Hajj pilgrims were normal practices of Arabs even about a hundred years ago.
To keep different tribes of Arabs united was always the most difficult task for the leaders/ruling class in Arabia. Bribing, marital alliance and giving share of loot could not ensure sufficient and long lasting loyalty from different tribes of Arabs. From Mohammad in 7th century to Abdul Aziz, the first modern day Arab king of Sa'udi Arabia who recapture Riyadh in 1902, all leaders faced the same problems.
Wahhab, a friend, philosopher and guide of earlier Sa'ud royalty in eighteenth century interpreted a very orthodox, intolerant and strict version of Islam and enforced it on Arab Muslims through Sa'ud patronage. This stringent form of Islam was reinstalled and reinforced by the Ikhwan movement of Al Artawiya in Arabia during second decade of twentieth century. Sa'ud family took advantage of Ikhwan movement also. The fickle minded Arabs were balanced to consistency with Wahhabism and Ikhwan movement.
With abolition of Caliphate during third decade of last century, Muslims of Indian sub-continent and other countries became anxious about the future of Islam. But in the next decade Wahhabism with support from Ikhwan movement and boom in oil exploration in Saudi Arabia gave new lease of life to Islam. This combination could resist the modifications and revisions which were brought to Islam in Turkey.
Wahhabism (and Ikhwan mevement) has been the fulcrum of oil diplomacy and Islamic diplomacy of Sa'udi Arabia through out the world since 1973. Bangladesh is a buring example of this fulcrum affect.