God has proven Himself that He is the only God in the midst of a nation that worshipped so many gods. That was in the land of Egypt. Egypt had so many gods. They did not believe in Jehovah. They did not believe in one god. They did not even know Him. They did service to gods who were not God. And God proved Himself to them. He humbled Egypt and silenced all their false gods.
The proof about God's existence is evidently declared in the entire world. They world has seen and had known what the power of God is. The decision not to believe in God is because men choose darkness over light. The light has come into the world but the world love darkness above the light because their works are evil.
The power of God proves His existence. We have witnessed in ourselves with what power how God has stepped into some situations in the present world and established his order. But we are not ready to believe in God. This is why humanity has decided to attribute the manifestation of God’s power to mere occurrences.