The history of nations is mostly characterized by ethnic and racial uniformity, not diversity.

Most national boundaries reflected linguistic, religious, and ethnic homogeneity. Until the late 20th century, diversity was considered a liability, not a strength.

Countries and societies that were ethnically homogeneous, such as ancient Germanic tribes or modern Japan, felt that they were inherently more stable and secure than the alternative, whether late imperial Rome or contemporary America.

Many societies created words to highlight their own racial purity. At times, “Volk” in German and “Raza” in Spanish (and “Razza” in Italian) meant more than just shared language, residence, or culture; those words also included a racial essence. Even today, it would be hard for someone Japanese to be fully accepted as a Mexican citizen, or for a native-born Mexican to migrate and become a Japanese citizen.

Many cultures reflected their suspicion of diversity by using pejorative nouns for the “other.” In Hebrew, the “goyim” were all the other non-Jewish nations and peoples. “Odar” in Armenian denoted the rest of the world that was not ethnically Armenian. For Japanese, the “gaijin” are those who by nationality, ethnicity, and race cannot become fully Japanese. In 18th-century Castilian Spain, “gringo” meant any foreign, non-native speakers of Spanish.

The Balkan states were the powder kegs of 20th-century world wars because different groups wanted to change national boundaries to reflect their separate ethnicities.

The premise of Nazi Germany was to incorporate all the German “Volk” into one vast racially and linguistically harmonious “Reich” — even if it meant destroying the national borders of Austria, Czechoslovakia and Poland.

The constitution of Mexico unapologetically predicates national immigration policies on not endangering Mexico’s ethnic makeup.