I will push my luck with some other questions:
Situation: France has fallen to GermanyUSA lands on French Morocco
a) There are French Troops there - do the USA place a Roundel and begin collecting income ?
b) There are No troops there - do the USA place a Roundel and begin collecting income ?
Regardless of whether there are French troops there, as long as you’re talking “French” Morocco, it will stay French until the Axis conquer it. The only way the US can ever own it, is to capture it from an Axis power that had first captured it.
Evolving Situation: Later France is liberated so the USA roundel is removed and control / income becomes French again, however there are both British and US troops ( no French troops) in say Southern France at the time of French Liberation.
Next Turn Germany reconquers France
Who gets the control of Southern France which contains both British, and US troops and a French Roundel?
Regardless of which Allied troops are in Southern France when France is liberated, and regardless which Allied power holds it at the time, control immediately reverts to France. So any cardboard roundels are removed, leaving only the French roundel that’s printed on the board. So France still has Southern France, even though it has little use for it.
This very situation is often a reason for the US and/or UK not to liberate France - or at least, not to hurry doing so. First, if they lose it again to Germany, the Germans will collect the French income. Second, before they liberated France, the other Allies (especially the US) could use the factories in Normandy-Bordeaux and in Southern France to produce much-needed units on the spot, and they lose that option (plus the IPC income) once those areas revert to France. So think twice before you rush in to have that triumphal march down Champs Elysees!