I wouldn't put the blame so much on Mexico as I would leftists in the USA. The leftists want revolution and are willing to import millions of foreign born to help them.
Take a look into Mexico’s government and you’ll just how organized it is on their part. They truly believe that it’s their right and their destiny to re-take the Southwestern US and they mean it. The Left here is their fifth-column, you’re right but it all originates from Mexico.