For the United States and its coalition partners to be able to crush the Islamic State (ISIS) once and for all, they should focus their attention on demolishing the caliphate's capital, Raqqa, in northern Syria.

To former US Army Major General and military expert Robert Scales Jr., this is the only way to completely defeat the jihadist organisation.

In an opinion article published on the Fox News website, Scales said the US should first and foremost solidify its partnership with its coalition partners in the campaign against the extremist group.

"The United States would be expected to build and lead a coalition of affected militaries that would include some NATO partners, such as Turkey, Britain and a few Eastern European armies. France would surely join," the military expert said.

"Coalition partnerships would likely include a host of Sunni military forces from Egypt, Jordan, Saudi Arabia and perhaps some Gulf states," he added.

He further proposed that the coalition should then consolidate its efforts to destroy Raqqa.

"In Iraq and Afghanistan we learned the painful lesson that disaster attends a campaign that has no achievable end. Unlike Al Qaeda, ISIS relies on territory for its legitimacy. Its vulnerable geographical centre of gravity is Raqqa, its capital in northern Syria," Scales said.

He added that massive airstrikes should be deployed over Raqqa, with the goal of cutting off food and water supply in the area, and to destroy all of ISIS' electronic portals.

"ISIS without Raqqa would be like Islam without Mecca or Catholicism without the Vatican. Denied its theological and ideological heartland, ISIS would become a criminal enterprise, rather than a state," the military expert said.

Scales further said that the anti-ISIS coalition should make sure that ISIS militants will not be able to return to Raqqa.

He also proposed the establishment of a joint Islamic "Kommandatura" or governing body to rule Raqqa after it is captured.