What major government structure did the United States adopt from Ancient Rome to prevent the concentration of power?

The major government structure that the United States adopted from Ancient Rome to prevent the concentration of power is the establishment of three branches of government. This framework is designed to provide a system of checks and balances, ensuring that no single branch—executive, legislative, or judicial—can dominate or misuse its authority. This principle was heavily influenced by the Roman Republic, which also featured a separation of powers to limit the reach of any one component.

In the Roman context, while the system had its own particularities, it exemplified the idea of distributing governmental responsibilities to foster balanced governance. By implementing a similar structure, the U.S. aimed to protect against tyranny and maintain liberty, echoing the concerns and experiences of the Founding Fathers who sought to avoid the errors of centralization seen in previous governments.

The other options reflect different forms of governance that do not specifically address the issue of power distribution in the way the three branches of government do. A unitary system centralizes power within a single governmental entity, direct democracy allows for majority rule without the nuanced protections of separated branches, and a constitutional monarchy combines a monarchy with political regulation but does not inherently ensure a system of checks and balances akin to that of the U.S. structure.