As George Friedman points out at Stratfor, there are two levels to what is happening in Bahrain. There are the legitimate complaints of the Shiite minority. And there's Iran's initiative to destabilize the Gulf in hopes of expanding its sphere of influence.

By sending troops to help the Bahrain government "calm" the Shia, Saudi Arabia has essentially checked Iran's initiative, at least for the time being. Friedman's analysis is characteristically sharp:

Saudi Arabia is leading a coalition force into Bahrain to help the government calm the unrest there. This move puts Iran in a difficult position, as Tehran had hoped to use the uprising in Bahrain to promote instability in the Persian Gulf region. Iran could refrain from acting and lose an opportunity to destabilize the region, or it could choose from several other options that do not seem particularly effective.

The Iranians clearly benefit from an uprising in Bahrain. It places the U.S. 5th Fleet’s basing in jeopardy, puts the United States in a difficult position and threatens the stability of other Persian Gulf Arab states. For the Iranians, the uprisings in North Africa and their spread to the Arabian Peninsula represent a golden opportunity for pursuing their long-standing interest (going back to the Shah and beyond) of dominating the Gulf.

The Iranians are accustomed to being able to use their covert capabilities to shape the political realities in countries. They did this effectively in Iraq and are doing it in Afghanistan. They regarded this as low risk and high reward. The Saudis, recognizing that this posed a fundamental risk to their regime and consulting with the Americans, have led a coalition force into Bahrain to halt the uprising and save the regime. Pressed by covert forces, they were forced into an overt action they were clearly reluctant to take.

You can read the whole thing here.