By no coincidence, that was also when Saudi Arabian troops arrived "to help the Government of Bahrain restore order". (Bahrain is an island connected to Saudi Arabia's Eastern Province by a long causeway.) Officially the Saudi soldiers were invited in by Bahrain's ruler, King Hamad bin Isa al-Khalifa. Unofficially, he probably had no choice in the matter.
Bahrain's ruling family is Sunni Muslim, like Saudi Arabia's and those of all the other members of the Gulf Co-operation Council (Kuwait, Qatar, United Arab Emirates and Oman). However, 70 per cent of Bahrain's population is Shia, whereas the rest of the GCC countries are overwhelmingly Sunni. And the relationship between Sunnis and Shias throughout the region is coming to resemble that between Catholics and Protestants in 16th-century Europe.
The ensuing century of religious wars in Europe was not really about doctrinal differences. The wars were driven by the rulers' conviction that people who did not share their particular brand of Christianity could not be loyal to them politically.
It was nonsense, but millions of Europeans were killed in the 1500s and 1600s in wars triggered by this belief. The same disease now seems to be taking root in the Arab Gulf states. Shias, it is argued, cannot be loyal to a Sunni ruling family. And if they object to being oppressed, it can only be because Shia-majority Iran has deliberately stirred them up.
There is a real political and military rivalry between Iran, the major power on the north side of the Gulf, and the smaller Arab states to the southwest. It has become worse since the US invasion of Iraq ended centuries of Sunni rule and put a Shia regime in power there. The competition is actually geopolitical and strategic, not sectarian, but people get confused.
So Saudi Arabia worries a lot about the loyalty of the large Shia population (maybe even a majority) in its Eastern Province, where all the oil is. It was certainly not going to tolerate a democracy - which it thinks would be a "Shia" democracy, and therefore a hostile regime - in Bahrain, right next door.
And, of course, it believed that the downtrodden Shia majority in Bahrain had been stirred up by Shia-majority Iran across the Gulf. So when Bahrain's King had still not got the pro-democracy protesters under control after an entire month, it sent its troops in.
It certainly wasn't what Crown Prince Sheikh Salman bin Hamad al-Khalifa intended: he was trying to negotiate with opposition parties about giving Shias a bigger role in the kingdom's affairs. But Saudi Arabia didn't want that kind of example right next-door, and it found hardline allies in the Bahraini royal family.
The triumvirate who are now running Bahrain are Khalifa bin Salman al-Khalifa, Prime Minister for the past 40 years, and the brothers Khalid bin Ahmed bin Salman al-Khalifa, the royal Court Minister, and Khalifa bin Ahmad al-Khalifa, who commands the Bahrain Defence Forces.
With them in charge, there will be no compromise, even though more than 80 Shia protesters have already been killed.
No Western government is going to condemn the country's rulers. That would seriously annoy Saudi Arabia, and they will never do that.
Gwynne Dyer is a journalist whose column is published in 45 countries.