Basing his argument in part on the past successes of the marketplace in assimilating and "Americanizing" immigrants, Joel Kotkin is sanguine about our multicultural future. Im encouraged, but wish that he had addressed the big difference between 19th and 20th century immigration, on the one hand, and the 21st century version, on the other. What happens when its easy to move back and forth between the old country and the new one. When my dad moved to California from the Netherlands in 1950, he knew that getting back home would be a rare event (though, thanks to the U.S. Army, it happened sooner than he anticipated). Now, theres much more travel and communication, which makes for a somewhat weaker incentive to give oneself wholly to ones new home.