What proves the oneness of God, and what prevents there from being more than one god, each with his own creation? Are the Quran's arguments for this convincing?

To the questioner who doubted the oneness of the Creator: Do not be surprised by mental doubts that lack proof. Begin by inquiring about the names, attributes, and actions of Allah. Whoever believes that Allah is the Creator of all things, and that He is the One, the Subduer, will not accept the multiplicity of gods. The "proof of mutual hindrance" (dalil al-tamanu') clarifies the impossibility of there being two gods; for if they differed in will, the universe would be corrupted, and if they agreed, that would indicate a deficiency in their power. The conception of multiple gods leaves the created being in bewilderment, choosing between worshipping all of them or worshipping the one who created him, leading to unavoidable complications. The assumption that the attributes of God could include imperfections such as lying and injustice contradicts reason and innate disposition (fitra). Instead of being preoccupied with far-fetched assumptions, reflect on the magnificent signs in the universe that point to the oneness and perfection of the Creator. The Holy Qur'an and the proven prophetic miracles in Islamic sources are sufficient proof for one who believes in divine messages.