All governments decline because the quality of the people who live in them declines first.
The men who inhabit a declining civilization have inferior intelligence, inferior character, inferior imagination, inferior drive, inferior judgement and inferior physiology. The politicians and leaders then come to reflect the low calibre of the citizens to whom their inferior message appeals.
The inferior man will always believe that the way to end his fear is to utterly surrender his legacy to authority. This is why all governments are always doomed to decline and collapse.
No matter how vibrant a nation begins or with what great stock in humans it is founded, it will always end the same way because every successful system gives rise to the conditions which will destroy it. The healthy and robust biological stock that is there at the birth of a country will be swamped and outnumbered by fast breeding mouthbreathers who will raise a generation that will isolate their children and their inheritance. Think about the movie PLEASANTVILLE, wherein America makes fun of the people of the 1950's because they were sincere and devoted and they did not have premarital sex. It's like standing on the deck of a sinking ship and laughing out loud at the navy rescue boats attempting to throw you a life preserver.
Nietszche was right. The last man blinks. "Formerly, the whole world was mad," he says and he smiles. He blinks again. It is in fact the last generation that is always insane.