He was not strong enough. He created the Vis (people), the classes of Devas which in their different orders are called Vasus, Rudras, Adityas, Visve Devas, Maruts.

In plain words: The story of creation goes on. Brahman, the one source of everything, still did not feel complete. So it made the common people among the gods. These are groups of gods called the Vasus, Rudras, Adityas, Visve Devas and Maruts.