Nicephorus, who needed large sums to strengthen his military force, set himself with great energy to increase the empire's revenue.
By withholding the tribute which Irene had agreed to pay to Harun al-Rashid, Nicephorus committed himself to a war with the Saracens.
By the death of Harun in 809, Nicephorus was left free to deal with the Bulgarian king, Krum, who was harassing his northern frontiers.
Krum is said to have made a drinkingcup of Nicephorus's skull.
He was frequently employed in missions to the pope, and in 968 to Constantinople to demand for the younger Otto (afterwards Otto II.) the hand of Theophano, daughter of the emperor Nicephorus Phocas.