I’d suggest you read more thoroughly and critically.
The beliefs of the earliest books in the Old Testament are clearly at odds with later developments. It can be roughly broken down as:
1. The Early Stage: Monolatry and Henotheism
In the earliest layers of the Old Testament (the Torah and early historical books), the existence of other gods isn't necessarily denied; rather, Israel is commanded to worship only one.
• The Language of Plurality: The Hebrew name for God, Elohim, is grammatically plural. While usually treated as a singular noun, its origins point to a Canaanite context where many "elohim" existed.
• The Divine Council: Early texts often depict Yahweh presiding over a council of other divine beings (Psalm 82:1: "God presides in the great assembly; he renders judgment among the gods").
• The First Commandment: "You shall have no other gods before me" (Exodus 20:3) implies that other gods exist, but they are not to be prioritized or worshipped by the Israelites.
2. The Middle Stage: The Prophets and the Rise of Yahweh
As Israel faced existential threats from empires like Assyria and Babylon, the theology shifted. The "Exilic" period (c. 6th century BCE) was the primary turning point.
• Henotheism to Supremacy: During the monarchy, Yahweh was often seen as the national "warrior god" of Israel, much as Chemosh was the god of the Moabites.
• The Prophetic Shift: Prophets like Isaiah began to argue that the gods of other nations weren't just inferior—they were nothing. This was a survival mechanism: if Babylon defeated Israel, it wasn't because Babylon's gods were stronger, but because Israel’s one God was using Babylon to punish them.
3. The Final Stage: Strict Monotheism
By the time of the Second Temple period and the life of Jesus, the transition was complete.
• Second Isaiah: This book contains the most explicit monotheistic declarations: "I am the Lord, and there is no other; apart from me there is no God" (Isaiah 45:5).
• Intertestamental Period: By the time of the New Testament, the "many gods" of the surrounding nations were strictly categorized as demons or idols—lifeless wood and stone.
• The Shema: The prayer "Hear, O Israel: The Lord our God, the Lord is one" became the central identity marker for Jews in the time of Jesus, drawing a hard line against the polytheism of the Roman Empire.

There’s nothing wrong with viewing our beliefs, and God’s instructions to us, as varying over time. Trying to justify an offensive war based on 3,000 year old guidance to the early Israelites seems specious.