I don't think the US would be as dominate as people think. It is cyclical for every country. Brazil has a massive population and similar demographics and Brazil hasn't won the last three tournaments. Before they won two of three tournaments from 94-2002, they hadn't won a World Cup in 24 years.
You can then take a country like Spain, with 45 million people and they may have had the most dominate run of any country in history from 2008-2012 winning to European championships and a WC.
The US Womens National Team is a good example of how hard it is to win those tournaments. The Womens team has the best players, the best athletes, the most dominant history and they have only won 2 of the 7 women's world cups.