Not long after he was elected president, Barack Obama arranged what senior US officials called "Terror Tuesdays".

On the agenda were "kill lists" — names of individuals whose perceived threat to America's security made them targets for assassination by unmanned drone attacks in Pakistan, Yemen, and Somalia.

The kill lists, scrutinised personally by Obama at the weekly meetings, were soon expanded to become what US journalist Jeremy Scahill, author of Dirty Wars, calls a form of "pre-crime" justice where individuals are considered fair game if they met certain life patterns of suspected terrorists.

Unidentified individuals, described as "military aged-males", would be targeted if they were at a certain place at certain times.

These are considered legitimate targets in "signature strikes".

How Obama embraced the hawks and the unaccountable and secretive Joint Special Operations Command (JSOC) left behind by the Bush administration is powerfully documented in Dirty Wars, published in Britain by Serpent's Tail this week.

"One of the enduring legacies of Obama's presidency is how he has normalised assassination as a central component of what is called America's national security policy", Scahill told me.

It has been easier for a Nobel Peace prize winning liberal Democrat to get away with drone strikes, prosecuting and persecuting whistleblowers, keeping Congress in the dark, than a Republican hawk, Scahill suggests.

Congress has not been able, or not wanted, to question the drone strikes, and polls show a majority in support of them.

"They are seen as a smarter, new way of cleaning up war", said Scarhill. That encouraged him to call the book, Dirty Wars.

He added: "I believe we are creating more new enemies than we are killing terrorists...And revenge is as powerful force".

Republicans, meanwhile, have chided Obama calling the drone strikes as an alternative to transporting and interrogating terror suspects at Guantánamo Bay.

Over the past decade, the US has ordered at least 300 drone strikes in Pakistan, Afghanistan, Yemen, Iraq and Mali, taking out some high level al-Qaida targets, but also killing some 2,000 civilians, according to the Bureau of Investigative Journalism.

In his eight years in office, Bush ordered about 50 drone strikes aimed at alleged terrorists. Obama is believed to have ordered nearly 300 in his first term as president.

The belated stirrings of a debate in the US will not be welcomed by the British government which has already tried to distance itself from the opposition drone strikes have provoked in Pakistan, Yemen, and elsewhere.

Britain's SAS has taken part in US special operations in what Scahill calls the CIA's "black-site archipelago" and British officials are likely to be in the loop, and even helping, US security and intelligence agencies in drone strikes ordered by Washington. Lawyers acting for the British government have already warned that any UK involvement will remain secret.

Drones are here to stay.

They are likely to be used more and more against targets in north, east, and west Africa, and elsewhere. Scahill subtitles his book, The World is a Battlefield.

Dirty Wars also chronicles in detail the life and death of Anwar al-Awlaki, an American killed by a drone strike in Yemen in September 2011 on the grounds that he was an influential al-Qaida supporter and operative.

His son, Abdulrahman al-Awlaki, a 16-year-old American boy, was killed in a drone strike a month later.