Good Day RickBurnett
I agree with Tulsitala Tom and Expand YourMind, whose answers I voted up. I would also add that there is the element of money. The principle thing couples get into serious conflict about is money, the household budget.
I think there are structural features about life in the United States that contribute to this, as opposed to what one would expect to find in Canada, some Latin American countries, and western Europe, where a more liberal Keynesian, social democratic order prevails -- where they have things like universal healthcare, free or much, much, cheaper college education, and a generally much more robust social safety net.
During economic tough times the social indicators always take a dip. But I am saying that even during relative good times economically, in the United States, the structural, "free market," nature of the economy puts stresses on people that they do not experience. Since the number one relationship bummer is money, that means that couples in the U.S. experience stresses that couples in social democratic countries do not face.
Did you see the movie by Michael Moore, called "Sicko?" What a disgrace that even Cuba, a tiny island against whom the United States has had sanctions going over forty years now, can nevertheless manage to provide her people, all her people with comprehensive, free healthcare, and America, the richest nation in the world, can't seem to manage it!