The effect of intensive selection over 12 years on the conformation of the Poland China Pig in changing from a lard to a bacon type (a) 1895-1912, (b)1913, (c)1915, (d)1917, (e) 1923.There's a book available for preview via Google called "Lawrie's Meat Science" that shows in pictures how the Poland China, the closest thing America ever had to a Mangalitsa, went from being a lard-type hog to a bacon-type hog. The rate of change is fastest in the first few years.
The 2007 version is a meat-type:
Although the modern version and the original have the same name, the economic and eating characteristics of the breed are completely different. Articles like this one often don't mention that the popular heritage breeds have changed with the times.
Ultimately, the demise of original Poland China can't be blamed on Con Agra, Smithfield, Big Agriculture, the government, etc. Americans simply stopped wanting such pigs, at which point the breed had to change with consumer tastes or vanish.
The Mangalitsa is essentially the same as it was in the 1800s. It was able to survive in its original form because the Hungarian government paid to preserve the breed when lard went out of fashion. Specific foods are important to Hungarians, some of them made from pigs, so they preserved the Mangalitsa. The breed survives now because people want such hogs. If consumer tastes change again and they go through a period of tremendous deprivation, perhaps the breed will again be at risk.
Given that the Hungarians had to spend so much money to preserve the breed (and how they almost failed), I'm skeptical that the critically endangered American breeds will survive very long. The expense of running a breeding program, in order to preserve genetic diversity, ensures that the animals will become gradually more inbred, making them even less economic and worth rehabilitating. It is hard to imagine the government or any entity finding the money, year after year, to pay to preserve biodiversity.