I did not see this comment last year, but have an interesting little tidbit to add regarding the decline of Rome and also our current situation.
The triumvirate of Caesar, Pompey, Sulla had an another interesting thread. Sulla was in his early fifties and feeling the start of decline. He was in charge of the eastern part of the empire, so he thought it would really be a feather in his cap to conquer further to the east like Alexander. He decided to go up against the Parthians, which I think was in the area of Iran and perhaps part of Afghanistan. He, his son, and his army were totally destroyed, but his young lieutenant Cassius managed to withdraw with about 10,000 troops back to Syria, which saved Syria from rising up against Rome.
Remember Cassius, “Yon Cassius hath a lean and hungry look, he thinks too much, such men are dangerous.” Will Shakespeare. At any rate, years later Cassius was a leader in the plot which killed Caesar, for “too much ambition.” Guess what Caesar’s too much ambition actually was. He wanted to go conquer the Parthians to avenge Rome’s good name. My take: beware all politicians who think that trying to conquer the Parthians, or their descendents, is a good idea. At any rate, check out Sulla and his campaign, a fascinating story of pride and failure.
But the rest of what you wrote of Crassus losing the battle of Carrhae (Harran -- the same place Abraham went to from Ur)
the Romans lost again in 259 to Shapur II of the Persian Sassanid empire. But between that time Trajan had destroyed the Parthian empire