The question of how to minimize or constrain the tyrannical impulses and corrupt practices of people wielding government authority has been examined extensively since the emergence of philosophy itself. I will forgo any attempt to summarize the arguments surrounding that topic and simply skip ahead to what I think is the best argument made so far. In a word, decentralization.
Keeping in mind that this is somewhat of a simplification, decentralization posits that political power should be maximally dispersed or diffused. Concentrated power almost always produces some degree of tyranny and corruption. For whatever reason, human nature is easily corrupted by power. Perhaps if you gave a monkey the same power as a president, he would also end up abusing it somehow. But I don't think anyone is going to deny that the more power a person has, the more liable they are to be corrupted by it. Decentralization addresses this problem by limiting the extent of political authority via localization. To reduce it to its most simple formulation, consider governments that are not allowed to govern more than 1,000 residents or 10 square miles of territory. In such situations, the government will never become powerful enough to tyrannize more than just a few people. And even if such a government were theoretically able to tyrannize its entire population of 1,000 residents, it would still be a relatively small amount of people. So decentralization will not eliminate tyranny, but it will place hard limits on its extent.
Another benefit of decentralization is that tyranny, should it come into being, is much easier to combat than a highly centralized form of tyranny. For starters, a localized government has less resources at its disposal. For obvious reasons, this makes it more difficult to crack down on resistance. For another, a localized government is, well, localized. For logistical reasons, it's much easier to influence a government when it is within walking distance of your house. And as a last resort, localized tyranny is much easier to escape. All you need to do is walk a few miles and you're in a different jurisdiction. Decentralization maximizes the amount of political choice that a person has.
One more benefit of decentralization is that it's more democratic. Mathematically speaking, it's basic logic. If you vote in an election with 999 other people, the smallest effect you could have an election is 0.1% (one vote out of a thousand). That may not seem like a lot, but consider just how insignificant your vote becomes when the electorate is in the millions or hundreds of millions.
None of this is to imply that decentralization is perfect. Only that it is a very good check on tyranny and corruption.