The article is not about the fall of the Roman Empire, but about the fall of the Roman Republic and its replacement with a dictatorship under Julius Caesar. The Empire expanded after that point.

Rome was bloodily founded, with the forced subjugation of other nations and peoples across what is now Italy.

The correlation seems less about the fall to ruin, but that that somewhere like the US would fall into a dictatorship and has many ingredients as Julius Caesar served to claim emperor. I would also add a hefty amount of backwards looking rhetoric also to the mix - things were better, more moral in the past; or we must address sins of the past. Putin has been using similar rhetoric to Caesar swapping the Ukraine for the Celts.

I recommend Dan Carlin’s Hardcore History on the Celtic Holocaust that poses that the whole expansion and annihilation of the Celts was a money making scheme by Julius Caesar to grasp power.