How did Rome build such a powerful empire

Through The Military Expansion.

Explanation:

Rome gave the people it conquered and others a form of roman citizenship, which enabled them to become roman citizens. As well as military expansion growing and developing the economy, bringing slaves, together with resources it received from conquered lands. Which roman people used to build their city and expand vastly.

china unilaterally claims the entire south china sea as sovereign territory, then builds artificial islands to bolster its claim. it suddenly activates an air defense identification zone over the east china sea, and threatens to down any aircraft that does not report its position. it builds roads into indian territory, then redraws the maps to show that it is actually chinese territory. the people's republic under president xi jinping is quickly becoming the bully of asia.