I think there are three aspects to it.
1) God has every right to rule the world according to His free will.
There is no higher authority God has to report to about how He rules the world. God is not wrong in ruling the world as He pleases, in fact, it is right for Him to rule it according to His will, for God is the Creator, the Owner, and the King over the creation.
2) God has enough power to rule the world according to His free will.
He is not lacking power in anyway to rule the world as He pleases. He is powerful enough to create, hold, and move every particle and every galaxy in the universe. He is wise enough to rule every moving creature including human beings according to His pleasure.
3) The creation is in fact ruled by God according to His free will in every way.
God, not only has the right and power to rule, but in fact rule the creation as He pleases and wills. He doesn't simply have a potential to rule over the world, He actually does rule the world exactly the way He wants. If the world is not run the way He wants, then God is still not sovereign, but only has potential to run it sovereignly.
Some may disagree with me here with my take on God's sovereignty, but I tried to keep this short and to the point. Any thoughts?