NEW YORK — Baruch Spinoza, the 17th-century Dutch philosopher, Benjamin Disraeli, the 19th-century British prime minister, and Nicolas Sarkozy, the 21st-century French president, have one thing in common: All were sons of immigrants.

People have migrated to other countries for thousands of years — to escape, prosper, be free or just to start again. Not a few enriched their adopted homelands by achieving great things or producing children who did.

New waves of immigrants are rarely, if ever, popular. But they are often needed. Many people have migrated to Western European countries from North Africa and Turkey during the last half-century, not because of Western generosity, but because they were required for jobs that natives no longer wanted. They were treated as temporary workers, however, not as immigrants.