LIKE some great empires of the past, the American empire may be heading towards decline due to "imperial overstretch" - a concept denoting that the US global empire has extended itself far beyond its ability to maintain its military or economic commitments.

Republican presidential candidate Donald Trump has not actually used the phrase, but he has implied that America is declining due to imperial overstretch, and as a remedy he advocates military and trade isolationism.

The idea of imperial overstretch (or imperial overreach) was presented by Paul Kennedy, a professor at Yale University, who believed that defence spending imposed such a crushing burden on the US that its decline was inevitable.