Monroe Doctrine
The Monroe Doctrine and "manifest destiny" formed a closely related nexus of principles: historian Walter McDougall calls manifest destiny a corollary of the Monroe Doctrine, because while the Monroe Doctrine did not specify expansion, expansion was necessary in order to enforce the doctrine. Concerns in the United States that European powers were seeking to acquire colonies or greater influence in North America led to calls for expansion in order to prevent this. In his influential 1935 study of manifest destiny, Albert Weinberg wrote: "the expansionism of the [1830s] arose as a defensive effort to forestall the encroachment of Europe in North America".