Final answer:
Option B, 'Buddhism spreading to Rome,' was NOT a reason for the fall of Rome. The decline was due to overextended military campaigns, internal political decay, and invasions by Germanic tribes and conflict with the Sassanids.
Step-by-step explanation:
The reason that was NOT a cause for the fall of Rome is option B: Buddhism was spreading to Rome and people changed their religion. The other options provided are historically accurate reasons contributing to Rome's decline. Rome did indeed spend too much money on wars to expand, which strained their resources (option A). The military, while not necessarily lazy, did become less disciplined and suffered from lack of funds and manpower, leading to weakened defenses (option C). And Germanic tribes did cross into Roman lands, causing significant pressure on the Roman Empire's borders (option D).
Rome faced myriad external pressures including invasions by Germanic tribes and conflicts with the Persian Sassanids, as well as internal disarray partly due to political corruption and economic difficulties. These issues were exacerbated by overextended military campaigns and a reliance on a robust but increasingly strained military force to control the empire's vast frontiers.