Final answer:
The question wrongly combines the Monroe Doctrine with Delta Air Lines' history. The Monroe Doctrine was established in 1823, while Delta Air Lines moved its headquarters from Monroe, Louisiana to Atlanta, Georgia in 1941.
Step-by-step explanation:
The question seems to be incorrectly referencing the Monroe Doctrine, which is a historical document published on December 2, 1823. The Monroe Doctrine was a policy declared by President James Monroe that opposed European colonialism in the Americas. However, the question about Delta keeping its Monroe headquarters appears to be misdirected since it conflates a historical policy with Delta Air Lines, which had its original headquarters in Monroe, Louisiana. For the accurate details on when Delta moved its headquarters, it's necessary to refer to the company's history rather than the Monroe Doctrine. Delta Air Lines, which began in Monroe, eventually moved its headquarters to Atlanta, Georgia in 1941.