When and why did the Sumerian writing arise?

On the territory of modern Iraq, when the Sumerians lived between the Tigris and Euphrates rivers. They invented cuneiform writing. In the beginning there was a system of signs, then a whole system, and then writing was invented. Historians date it to 3,500 BC. Archaeological finds in about 3300 BC clay tablets are evidence of this. With a special stick with a tip, signs were applied to raw plates and tablets. The development of writing was necessary for the rapid development of the cities of the Sumerian kingdom.