He tried to stay out of secular political matters and focus his energy on the good of the Church, but was greatly influenced by the Colonna faction in Rome.
Crowned Charles II king of Naples and Sicily on 29 May1289 after Charles agreed to loyalty to the Vatican.
He issued a constitution on 18 July1289 that gave new financial control to the college of cardinals, making them much more independent.
For years Nicholas quietly laid the groundwork for Crusade, but the loss of Ptolemais in 1291 led him to call for Christian princes to reclaim the Holy Lands.
He outfitted twenty ships, preached the Crusade, and made plans, but his appeals were ignored.
He preached against heresy, and particularly condemned the Apostolici in 1290.
He dispatched missionaries to Bulgaria, Ethiopia, and China, and financed building and artistic programs in Rome.