Bloody Sunday

On May 2, 1970, at Kent State University, the Ohio National Guard was called in to contain a student protest against the American invasion of Cambodia. On May 4, National Guard troops fired into the crowd, killing four and wounding nine others.

On June 13, 1970, President Nixon established the Scranton Commission, which issued its findings in September 1970, concluding that the Ohio National Guard shootings were unjustified and that "The Kent State tragedy must mark the last time...loaded rifles are issued to guardsmen confronting student demonstrators."

Posse Comitatus already prohibits the US military from being used for domestic law enforcement, although there is an exception for National Guard troops under a state governor.

Now compare that to...

On January 10, 1972, in Derry, Northern Ireland, the British Army Parachute Regiment opened fire on a civil rights march. Thirteen people, seven of whom were teenagers, were killed, while 14 more were injured. (One later died.) Five of those wounded were shot in the back.

An inquiry was called and, in April 1972, concluded "there would have been no deaths if there had not been an illegal march."

In January 1998, on the 26th anniversary of what came to be known as "Bloody Sunday," Prime Minister Tony Blair announced a new inquiry. In 2000, the inquiry opened with 116 days of public hearings. The judges retired in November 2004. In February 2008, the Secretary of State revealed that the inquiry was still costing £500,000 (US $750,000) per month. The report was expected in 2008, but on November 6 of that year, the chairman announced the report would take at least another year. In 2009, this was pushed to March 2010. It has not been published yet. The total cost for the inquiry is now over £200 million (US $300 million), more than half of the cost is believed to be legal bills.

The UK still has no restrictions on deploying the military against its own people.