The shifts in the American approach towards Salisbury were reflective not only of the personal beliefs of the individuals in the White House but represented the larger diverse pressures shaping foreign policy during the period of the Unilateral Declaration of Independence (UDI). Domestically, the Rhodesian UDI era, spanned a period of social and political change within the United States. A number of historians, notably John Lewis Gaddis, have argued that the containment of global Communism was the principal concern of policy makers during the entire Cold War era. In the view of white Rhodesia, communism was insidiously spreading throughout Africa and London was doing little to prevent it. The high levels of American direct and indirect investment in South Africa and the predominance of Western companies in the apartheid economy have been documented by historians.