Answer: what links these two peoples together is Enlightenment and all values associated with it. It has its significant role today as well.
Explanation: For French Englightenment and resulting French revolution is really a turning point of their history (storming of the Bastille, July 14, is national feast in France). For Americans it is the same because American revolution, Proclamation of Independence and American constitutionalism were in fact a product of Enlightenment and especially French Enlightenment. Moreover, it was Enlightenment culture in France that produced something called "engaged intellectual", i.e. politically and socially active intellectual which plays a crucial role in French civilization. The same can be said about American Founding father who can be considered "engaged intellectuals". Of course there are many differences, for ex. French traditional Catholicism.
Two landforms that can isolate and protect a civilization are mountain ranges and seas. Mountain ranges block invaders as they are hard to ascend and require invades to find a detour, thus prolonging the invasion. The sea is another barrier because the sea can be dangerous and so vast that people can get easily lost.
