American foreign policy from the time of nation’s 5th President (James Monroe) through to the present can be seen through the prism of the Monroe Doctrine of 1823. Not fully understood as a doctrine at the time, it became so a generation later. It was meant as a warning to Europe against further colonization of the Americas. 

Later, in 1904, under President Theodore Roosevelt, who more punitively wanted it as a bulwark against barbarism, a corollary was added. 

A further congressional re-reading following WW1 was undertaken in relation to the League of Nations, which, had America signed up to, would have given foreign powers some say over deploying American troops for peace keeping missions, thus contravening the Doctrine or how the doctrine was being interpreted at that point.