God often works out his purposes through large empires. He used Babylon to bring judgement against Israel. He then used the Medes to bring judgment against Babylon. God called Cyrus to accomplish his purposes.
This is what the LORD says to his anointed,to Cyrus, whose right hand I take hold of tosubdue nations before him and to strip kings of their armor,to open doorsbefore him so that gates will not be shut (Is 45:1).
God uses human empires to execute judgement on evil nations, but they are not the optimal form of Government.
We always face a choice between the government of God and the government of man. When we reject God, we end up with the government of man. Some human governments are weak and pathetic, but all human government has a tendency towards accumulation of power. Under human government, state power grows and eventually swamps everything. The fourth beast of Daniel is ultimate triumph of state power.