Hi /u/alpinestarskid - Just to clarify, did you mean 1940 as written in your title, or did you mean to ask about 1840?

If you are referring to 1940, it might be useful to clarify what sort of 'control' you're referring to - obviously, Mexico in 1940 had no formal control over any territory which is currently part of the United States. Would you be referring to 'influence' as opposed to formal control?