Ummm, things have changed substantially from that time. I hope you are able to stragegize from current circumstances. -- Since then, the Monroe Doctrine has served us well ... --
The Monroe Doctine involved a geographic limitation. We have NOT been following it.
-- I prefer that hostiles not even contemplate invading America ... --
Me too, but they are here. My strategy involved massive destructive deterrant (nukes), and a "FU" attitude among a fighting populace.
-- the best way to do that is to keep our troops [away from the country] --
I disagree, moneyspender.
We have been following the Monroe Doctrine since its inception. In the 1800s, the threat to us was from foreign powers using South and North America as a base to attack us from. Since then, we have made it progressively harder for foreign powers to do that by first winning the Mexican-American War, then purchasing Alaska and ultimately at the end of the 19th century by annexing Hawaii.
However, technology has made the world smaller and the Atlantic and Pacific oceans are not the barriers they used to be - as was perhaps best demonstrated when the Japanese attacked Pearl Harbor.
As a result, because technology has made the world smaller, the geography covered by the thinking behind the Monroe Doctrine has progressively gotten bigger.