After reading through that list of Mexicans in MLS, I wondered if more Mexicans have played in MLS than any other nationality. The only country I could think of that has sent a lot of players here is Argentina. Maybe DC United's Argentine pipeline skews my thinking but there have been such notable players as Silvio Rudman and Marcelo Herrera in the past.
I have a very cool MLS Record and Fact book. It has a player registry that includes any player who has played even one minute in MLS with their picture, date and place of birth and career stats, which is how I came across Rudman (191 minutes for Columbus in 1997) and Herrera (17 starts for Miami in 1998).
For instance, I flipped to page 434 and the players on that page are:
Johnny Torres (New England from 98-00, Miami 00, New England 01, Chicago 02)
Jake Traeger (15 minutes combined in 03-04 with Columbus)
John Jairo Trellez (792 minutes with Dallas in 1999, 3 G, 2 A)
Seth Trembly (Colorado 2000-04, RSL 05)
Steve Trittschuh (13,594 career minutes with Colorado and Tampa Bay)
Mickey Trotman (the late great one)
Taylor Twellman (born 2/29/80 in Minneapolis)
Of that group, Torres and Trellez were born in Colombia, Trotman in Trinidad and the others in the US and A.
I could flip through every page and list all the Argies but that seems like a daunting and fruitless task. I'm not that interested, just saying, it'd be nice to know.