The Self-create Brahman created the Brahmana and the Kshatriya. They have a common origin. If they apply their energies separately, they would never be able to keep up the world.
ब्रह्मक्षत्रमिदं सृष्टमेकयोनि स्वयम्भुवा। पृथग्बलविधानं तन्न लोकं परिपालयेत्॥