The French aided the Americans in their revolution against their British oppressors. Now Benoît Pous-Bertran de Balanda, the descendant of a French general who fought for the Americans, is trying to help his wealthy countrymen escape what he calls the tyranny of a new Socialist government primed to severely tax the rich. And France’s loss could be New York’s gain. Mr. Pous-Bertran de Balanda, 30, is a broker for wealthy French clients looking to buy apartments in Manhattan. With the election of the Socialist François Hollande as president this month, the wealthy in France are suddenly scrambling for places to...