“Surely God is with you, and there is no other; there is no other god”. 
Isa 45:14 NIV 

There are many religions in the world today. Christians number about two and a half billions, Muslims about one and a half billion. There are approximately a billion Hindus, half a billion each who follow Taoism and Buddhism. About a billion profess no religion. About fourteen million adhere to the Jewish faith. In some countries there is complete freedom of religion, in some there is partial freedom and in some there is no freedom. 
In Isaiah’s day the effectiveness of any nation’s god was measured by the nation’s wealth, the power of the king and of the nation, and the military success or defeat in international conflict. In Isaiah’s context, the rise of the Persian Empire would indicate that its gods were strong. That is what is behind his claim that when in the future the Persians had restored the Israelites to Israel, the people of other nations would see what a great God Israel had and would come to worship him. They would see that Jehovah God had restored his people and had made them great – and therefore he was great. They would even come to see that the rest were not gods at all. We have no evidence that this really happened. But the Jewish faith did spread when Jews migrated to follow business interests and set up synagogues wherever they went. Some Gentiles joined them and worshipped Jehovah God. 
When the Christian faith was spread by Paul and the other apostles, both Jews and Gentiles joined the Christian Church, saying in effect “There is no other God”. Isaiah’s dream had finally come true. 

“There is no other name under heaven given to men by which we must be saved”.
Acts 4:12 NIV