The Roman Empire decline started from the fourth to fifth century. The main causes were: economic and demographic crisis, the crazy morality and an immigration without control that were able to damage a great and secular empire.
If we compare the actual situation in Europe with the fall of Roman Empire we can see that there are some commonalities. In fact, the economic Roman crisis started with similar characteristics to the actual one. The livelihood of Roman people were reduced and so also the amount of people started to decline. In this situation, the only thing that the Roman Empire did was to increase taxes.
The demographic decline wasn’t analyze in its deep causes and the solution was to introduce the necessary labors from abroad, as it is happening nowadays. However, the integration in the Roman Empire became an invasion, above all Goths tried to rise up against the Empire.
Therefore, the intention to integrate barbarians wasn’t easy and it was a failure.