What event in AD 280 contributed to the political shape of modern China?

The event in AD 280 that significantly contributed to the political shape of modern China is the unification under the Western Chin dynasty. This period marked a pivotal moment in Chinese history, as it was during the Western Chin dynasty that China was brought under a centralized rule, facilitating the consolidation of power and cultural unity among its territories. The dynasty's emphasis on a centralized government laid the groundwork for subsequent dynasties and helped establish the framework of governance that would influence China's political landscape for centuries.

The Western Chin dynasty played a crucial role in standardizing laws, currency, and measurements, which aided in creating a unified Chinese identity. This era also saw advances in infrastructure, such as road construction and the development of trade networks. Such foundations were instrumental in shaping the China we recognize today.

The other options correspond to significant historical events, but they pertain to different regions and contexts. The birth of Muhammad is crucial to the history of Islam and the Middle East, the signing of the Magna Carta relates to English constitutional history, and the fall of the Roman Empire primarily influenced Western Europe. Thus, the unification under the Western Chin dynasty is distinctly relevant to the formation of modern China.