It should have been a routine traffic stop.

A motorist, who was not wearing her seatbelt, was pulled over. In less than 15 minutes the encounter ended with a police officer smashing an axe through the car window and using a Taser on the front seat passenger.

The incident would have gone unnoticed but for the fact that one of the woman’s two children in the back filmed the incident on his mobile phone.

This was just one of a series of confrontations between black Americans and white officers in recent months in which the police seem all too ready to respond with disproportionate force.

Unease about the police is not restricted to the liberal left.

Rand Paul, the libertarian Republican senator for Kentucky and a possible presidential candidate, warned about what he described as the militarisation of the police in Time.

He warned that towns were competing for surplus military equipment from the Federal government to build up their own small armies.

“When you couple this militarisation of law enforcement with an erosion of civil liberties and due process that allows the police to become judge and jury – national security letters, no-knock searches, broad general warrants, pre-conviction forfeiture – we begin to have a very serious problem on our hands,” he wrote.

“Given these developments, it is almost impossible for many Americans not to feel like their government is targeting them.

“Given the racial disparities in our criminal justice system, it is impossible for African-Americans not to feel like their government is particularly targeting them.”

Senator Paul’s remarks followed fatal shooting of Michael Brown, an unarmed black teenager by a white officer in Ferguson, Missouri on 9 August. According to several eyewitnesses he had his hands up when the police officer opened fire.

Fuelled by the social media, the black community in Ferguson reacted furiously, triggering some of the worst riots seen in America for decades, with protests spreading to around 60 other cities.

This was hardly an isolated incident. New research by ProPublica showed an alarming racial disparity in the chances of being killed by the police.

Examining 1,217 fatal shootings, it found that black teenagers were killed at a rate of 31.17 per million and their white counterparts, 1.47.

Public opinion is swinging against the police with a Pew public opinion poll showing that the majority of Americans felt treated racial groups differently and did not use an “appropriate amount of force”.

Given events over the last few months, the results are hardly surprising.

Four days before the killing of Michael Brown another African-American, John Crawford, 22, was shot dead by police while talking to his girlfriend on a mobile phone. He was carrying a toy gun he had just bought at a shopping mall in Beavercreek, Ohio.

A grand jury refused to indict the two officers involved.

In July Eric Garner, a father of six, died after being arrested and subdued in a chokehold in New York – a tactic which is in fact outlawed by the city’s own police department.

Earlier this month, Ernest Satterwhite, 68, was killed in his own driveway in North Augusta, South Carolina following what local media described as a low speed nine-mile pursuit.

His offence was refusing to pull over for the police officer – something he had done on a number of previous occasions.

The officer said that Satterwhite made a grab for his gun, though apparently there was no evidence to back that up.

Again prosecutors tried to act, but as with the Crawford case, the grand jury refused to press a charge of voluntary manslaughter.

Other incidents may have not ended fatally, but have still been pretty horrific such as the repeated shooting of Levar Jones on September 4 in South Carolina.

Jones, 35, had just pulled into a filling station when he was confronted by a state trooper, who suspected that he was not earing a seatbelt.

Jones was ordered to produce his driving licence but was then shot repeatedly when he reached into his truck to fish it out.

On this occasion the whole thing was caught on film by the dashboard camera in the state trooper’s car and it is not pretty viewing.

The officer, Sean Groubert, has been sacked and is facing aggravated battery charges. His defence was that he saw something black in Jones’s hands – it was his wallet.

David Millward is a US correspondent for the Daily Telegrpah