Complex sentence: With the Spaniards'position consolidated by Almagro's reinforcements, Manco Inca decided that Ollantaytambo was too close to Cusco to be tenable so he withdrew further east to the town of Vitcos.
Split into simpler sentences: With the Spaniards'position consolidated by Almagro's reinforcements, Manco Inca decided that Ollantaytambo was no longer tenable as it was too close to Cusco. So he withdrew further east to the town of Vitcos.