The term "Manifest Destiny" was coined in 1845. According to this concept the United States was destined to expand westward across the whole continent and spread its values (democracy and capitalism). "The attitude behind Manifest Destiny had long been a part of the American experience. The impatient English who colonized North America in the 1600s and 1700s immediately gazed westward and instantly considered ways to venture into the wilderness and tame it." (Encyclopaedia Britannica). In his 2020 State of the Union speech, President Trump declared: "In reaffirming our heritage as a free nation, we must remember that America has always been a frontier nation. Now we must embrace the next frontier: America’s manifest destiny in the stars." Here, Trump refers to two founding myths that all Americans readily recognise : that of Manifest Destiny and the Frontier. Many political opponents were outraged by these references and reminded people that the concept of Manifest Destiny had been used to justify the genocide of Native Americans. The idea of a "new frontier" echoed Kennedy's acceptance speech at the Democratic Convention in 1960: "We stand today on the edge of a New Frontier—the frontier of the 1960s, the frontier of unknown opportunities and perils, the frontier of unfilled hopes and unfilled threats. ... Beyond that frontier are uncharted areas of science and space, unsolved problems of peace and war, unconquered problems of ignorance and prejudice, unanswered questions of poverty and surplus."
Originally "The Frontier" was an imaginary border between the lands that had been colonised by white people and the wilderness. As white settlers moved west, so did the Frontier. According to Turner, a 19th century historian, the Frontier shaped American society and its values. A contemporary historian explains that by the beginning of the $20^{th}$ century, the Frontier had become a "state of mind, …, a cultural zone, … a type of society."
Trump may refer to the Frontier but according to some historians, he misunderstands the concept. A New York Times article published on March 4 2019 explains that : " the historian Greg Grandin argues that America’s urge to wall off its borders marks the death of our most potent myth—the galvanizing vision of men and women seeking freedom along a vast frontier, a space for reinvention, unburdened by society, history, and one’s own past." In other words, by building a wall between the US and Mexico, Trump is killing the frontier.
The USA is not the only country with an isolationist agenda. A politician described Brexit as "the most isolationist deed in the last century for Britain". Many people in the UK and Europe would agree that Brexiters, as they were called, voted massively first of all to end freedom of movement. Immigration in the UK, like in the US and other parts of the world has become a contentious issue.
