The factor that most greatly limits the power of the US government is a constitutional system.
The Constitutional system is based on the division of powers in the federal government. The system of checks and balances does not allow any federal branch to have more power over the others. The three branches check each other in the US government. The executive branch is represented by the President, the legislative branch by US Congress, and the judicial branch by the US Supreme Court.
Constitutional system because the government, when setting up rules or laws or anything of the sort, it would have to abide by the Constitution which limits the governments power.
