When the Assyrians collected tribute from conquered peoples the empire became stronger because why

We first hear of the Assyrians around 2300 BC, when Sargon of Akkad invaded their small kingdom to the north which was well-known traders, who traveled constantly between Assur and southern Turkey. When they had war, they took the weapons of the conquered and the value items of the cities.

Tribute is monetary benefit conferred for protection. Money causes the receiver of the money to be able to acquire more things. Therefore, paying tribute to Assyria led to a strengthening of the Assyrian Empire.