One of the casualties of the recent ISIL (Islamic State in Iraq and the Levant) attacks in France and Belgium was the reputation of Saudi Arabia as an ally in the fight against ISIL. The media were all over the state of Islam in Belgium and many little-publicized facts were made very public. Chief among them was the role of Saudi Arabia played in building (at Saudi expense) mosques and religious schools in Belgium and then staffing them. These facilities were controlled by very-conservative (and anti-Western) clerics and religious teachers who were often trained in Saudi Arabia. This should not be surprising as since the 1980s Saudi Arabia has spent over $100 billion doing this promotion of the very conservative Wahhabi form of Sunni Islam that has predominated in Saudi Arabia since the 18th century.
This was all made possible after 1970 when the Arab oil states, mainly Saudi Arabia, found themselves with unexpected and unprecedented oil wealth. That was the result of the formation of the OPEC oil cartel. Because of OPEC the price of oil went from $3 a barrel in 1970 to $35 a barrel in 1980. Suddenly it became possible for Moslems to show how pious they were by funding Wahhabi missionaries who went to other Moslem (and many non-Moslem) nations to preach, establish Wahhabi religious schools and mosques and create the current Islamic terrorism problem. Billions were (and still are) spent on this and the policy of getting the young boys into these free religious schools and turning many of them into hateful (towards anyone not like them) Islamic religious fanatics led to a major outbreak of Islamic terrorism in the late 20th century. Saddam Hussein (as did many other Moslem dictators) kept this out of Iraq until 1991.
This Saudi effort was spectacularly successful in Brussels where over 20 percent of the population is now Moslem and most of them are Wahhabi Sunni. You could see this coming in the late 1970s when Saudi Arabia financed the rebuilding of the old mosque there into the Great Mosque of Brussels. This rebuilt mosque opened in 1978 and became the core of an Islamic Cultural Center that ran schools and efforts to convert Christians to Islam. All the teaching was done by clerics and instructors following the Wahhabi view of the world which believed all non-Moslems were a danger to Islam and must be eventually converted or killed. When criticized about this the Saudis got away with explaining it as “cultural differences.” Yet when data was compiled about the origins of ISIL recruits from Europe it was found that Belgium had the highest per-capita number of ISIL volunteers. No surprise that many who returned (nearly half died in Syria and Iraq) were even more determined to bring the war to Belgium. At this point Belgian officials were forced to admit that many Belgian Moslems had complained to the government about all this anti-Western preaching and were ignored because it had long been Belgian policy not to offend the Saudis.
Even before 2015 some Saudi diplomats were expelled for being too enthusiastic, and blatant, about Saudi support for thing kind of teaching but there was never an effort to shut down the schools or pro-Islamic terrorism preachers. While many Belgian Moslems sought to become Westernized, at least so they could get an education that would result in a job, most of those exposed to the Wahhabi preaching refused to make themselves employable and then complained that Belgium was punishing them for being Moslem.