Question: Who define Mexico to "be the melting pot of all races?"
About the article "Mexico", section "Culture".

Candidate passages:
The melting pot is an analogy for the way in which heterogeneous societies become more homogeneous.
Melting pot may also refer to:  Crucible, a container in which materials can be heated to very high temperatures  The Melting Pot (restaurant), an American chain of fondue restaurants  
The Melting Pot is a chain of franchised fondue restaurants in the United States, Canada and Mexico.
The Tampa, Florida based company had 142 locations as of August 2009, with 28 more locations under development.
The Melting Pot menu contains various cheese fondues, wines, salads, entrees of meat and seafood served with dipping sauces and oil or broth to be cooked in, and chocolate fondues.
It is part of Front Burner Brands. 
  The melting pot remains a stock phrase in American political and cultural dialogue.
The general perception of its process and effects can be summed up in "The Great American Melting Pot" song from "Schoolhouse Rock!".
In 1969 the song "Melting Pot" was released by the UK band Blue Mink and charted at #3 in the UK Singles Chart.
The lyrics espouse how the world should become one big melting pot where different races and religions are to be mixed, "churning out coffee coloured people by the score", referring to the possible pigmentation of children after such racial mixing.
On The Colbert Report, an alternative to the melting pot culture was posed on "The Wørd" called "Lunchables", where separate cultures "co-exist" by being entirely separate and maintaining no contact or involvement (see also NIMBY).  
Zangwill supported the feminist and pacifist movements, but his greatest impact may have been as a writer who popularized the idea of the melting of the races into a single, American nation.
The hero of his widely-produced play, "The Melting Pot", proclaims: ""America is God's Crucible, the great Melting-Pot where all the races of Europe are melting and reforming... Germans and Frenchmen, Irishmen and Englishmen, Jews and Russians - into the Crucible with you all!
God is making the American."'"
The melting pot theory of ethnic relations, which sees American identity as centered upon the acculturation or assimilation and the intermarriage of white immigrant groups, has been analyzed by the emerging academic field of whiteness studies.
This discipline examines the "social construction of whiteness" and highlights the changing ways in which whiteness has been normative to American national identity from the 17th to the 20th century.
In the late 19th and early 20th centuries, European immigration to the United States became increasingly diverse and increased substantially in numbers.
Beginning in the 1890s, large numbers of Southern and Eastern European immigrant groups such as the Italians, Jews, and Poles arrived.
Many returned to Europe but those who remained merged into the cultural melting pot, adopting American lifestyles.
By contrast, Chinese arrivals met intense hostility and new laws in the 1880s tried to exclude them, but many arrived illegally.
Hostility forced them into "Chinatowns" or ethnic enclaves in the larger cities, where they lived a culture apart and seldom assimilated.
The acquisition of Hawaii in 1898, with full citizenship for the residents of all races, greatly increased the Asian American population.
In the early 20th century, the meaning of the recently popularized concept of the melting pot was subject to ongoing debate which centered on the issue of immigration.
The debate surrounding the concept of the melting pot centered on how immigration impacted American society and on how immigrants should be approached.
The melting pot was equated with either the acculturation or the total assimilation of European immigrants, and the debate centered on the differences between these two ways of approaching immigration: "Was the idea to melt down the immigrants and then pour the resulting, formless liquid into the preexisting cultural and social molds modeled on Anglo-Protestants like Henry Ford and Woodrow Wilson, or was the idea instead that everyone, "Mayflower" descendants and Sicilians, Ashkenazi and Slovaks, would act chemically upon each other so that all would be changed, and a new compound would emerge?
"Nativists wanted to severely restrict access to the melting pot.
They felt that far too many "undesirables," or in their view, culturally inferior immigrants from Southern and Eastern Europe had already arrived.
The compromises that were reached in a series of immigration laws in the 1920s established the principle that the number of new arrivals should be small, and, apart from family reunification, the inflow of new immigrants should match the ethnic profile of the nation as it existed at that time.
National quotas were established that discouraged immigration from Poland, Italy and Russia, and encouraged immigration from Britain, Ireland and Germany.