Decline of Ancient Rome

Political

Unrest from the lower class -
As the Roman government began to implement more tax laws (such as the ones that didn't allow farmers and business owners to leave their farms and businesses), unrest began to grow amongst the lower classes within the Roman empire.

Weak and incompetent Emperors -
The last great emperor of Rome was considered to be Marcus Aurelius, and afterwards the Roman Empirical system began to fall apart. All the Roman emperors during the decline of Rome were weak and incompetent, and did not stay in power for very long. At one point, there was a 50 year period where a total of 26 emperors were put into power. With their main power being so unstable, it is understandable that the empire itself was as well.

Splitting of the Empire
In 395 CE, the Roman Empire split into the Eastern and Western Roman Empire, each of which was governed by its own Emperor. The Eastern Empire, however, was decidedly stronger both economically and poltically (and would later become the Byzantine Empire), the Western Roman Empire was much weaker and would eventually succumb to outside attacks and a weak economy.

Fighting Over Succession
Another problem in the political scope of the Roman Empire was division due to the battles over succession. Civil wars and battles were frequent. and caused division between the people of Rome. After Trajan's reign, more people who were not of Italian descent wanted to become emperor, making battles for succession even worse and causing more division.

Due to constant fighting over succession, emperors were often assassinated in order for others to come into power, which contributed to the weakening of the imperial system in Rome.

Economic

Military

Mercenary Armies -
Romans began to use mercenary armies called foederati in their military, which were made up of the Germanic tribes that were allowed to settle within the Roman border. The problem with this was the fact that because these were mercenaries hired by Rome rather than actual Roman soldiers who fought and defended Rome because it was their home and country, these armies had little to no loyalty to Rome.

Size of the Roman Empire -
The Roman Empire grew to such as large size that it became difficult to guard and defend all at once, especially considering the dwindling loyalty in the Roman army (mercenary soldiers) and decliine of the rest of the Roman military (poorly trained and equipped). This made Rome vulnerable to attacks from all sides of the borer.

Invasions from the Huns -
The huns were a rising power coming in and attacking the west of Rome. Under their leader, the king Attila, the Huns made many attacks into the Roman Empire.

Invasions from the Huns also caused the Germanic tribes to have to flee to Rome, which was the catalyst for everything they did within the Roman border (e.g. multiple sackings of Rome.)

Letting Germanic Tribes in Roman Borders -
Germanic tribes outside of Rome had less and less territory as Rome began to expand more, and then finally they were pushed again by the Huns. They fled to Rome for safety, and the Romans let them into their borders. The Romans, however, treated these tribes very poorly, and this led to lots of conflict and eventually to tribes such as the Goths and Vandals to sack Rome.

The decline of the Roman trade routes was mainly caused by the constant warfare between the Romans and the Germanic tribes, as well as the fact that these tribes constantly pillaged and destroyed things such as trade routes, farms etc.