All of the listed factors contributed to the increased economic and military power of the Sumerians. However, if you have to choose one that stands out as particularly significant, it would be:
the development of bronze to make weapons.
The advancement in metallurgy allowed Sumerians to create more effective weapons and tools, which greatly enhanced their military capabilities and contributed to their overall power. Nonetheless, the combination of all these factors played a crucial role in establishing Sumerian dominance in the region.