What governmental changes took place in Animal Farm?

I think that the question might need a bit more
specificity to it in order to yield the most effective of answers.  One of the most
significant changes that ends up happening in terms of government is the structure of
the pigs being on top of the political hierarchy is a significant governmental change. 
It is significant because it is the first establishment of a ruling class of animals,
and a distinction between the animals in that "some are more equal than others." 
Another significant governmental change is the evolution from a dual leadership role of
Snowball and Napoleon, to a singular one with the latter running off the former.  This
helps to consolidate power into one entity, allowing power to come from top down in the
most deliberate of ways.  Another governmental change is the slow alteration from a
collective political order to one that professes to be collective, but rather acts in
the interests of one particular element.  The pigs constantly speak to the idea of
acting in concert with the interests of all, but as the novel develops, it becomes
painfully evident that only the pigs and the dogs are succeeding in this political
order.  All else are subservient, indicating a significant governmental
change.