How was Abd al-Rahman III ruthless and successful?

Abd ar-Rahman III was the most prominent representative of the Cordoba Umayyad dynasty, governing from 912 to 961. He assumed power during the period when the emirate of Cordoba was a city-state of little importance in al-Andalus. However, he quickly rebuilt the position of the Umayyads in the Iberian Peninsula, regaining the lands lost as a result of uprisings and rebellions. From 912 he waged constant wars with local Muslim rulers and rebel leaders.

In 917, he began his expansion in North Africa, thereby counteracting the policy of the Fatimid caliphs in the Maghreb. He was paid tribute by Morocco, Melilla and Ceuta. In 917, he declared a holy war against Leon, which invaded his emirate. Over time it was turned into jihad and kital against all Christian rulers in the Iberian Peninsula.  In 924 he captured and destroyed Navarre. His march north was stopped only by a severe defeat in 939 at Alhandega.

He was a skillful politician in the emirate's internal affairs. He pushed away the Arab aristocracy, which was striving for an oligarchy in the state. When he was sure of his absolute power, on January 16, 929, he assumed the title of caliph and ordered that his name be mentioned during each prayer.  During his reign, the economy and agriculture of al-Andalus developed. The caliph led to the expansion of the mines of precious metals. He developed in Spain the production of weapons, glass, brass and silkworm farming.