The war began with equal fortune at first to each side, but later fortune turned in favor of the Swedes, while food grew scarce in Christian's army, his foragers being beaten back wherever they appeared. Soon, with an army dwindled to two thousand men, he was forced to march back to Obslo.
So far Gustavus's army had been fighting alone, and it was not until March, 1532, that some Danish ships of war arrived. But their coming soon ended the war. They burned Christian's vessels and reinforced Aggerhus, and in May sailed towards Obslo.
Christian's hopes of success were now at an end. He had made his final effort and had failed. His men were forsaking him in troops and resistance to his foes became impossible. As a last resort he tried a crafty expedient, contriving to get some forged letters distributed in the Danish camp to the effect that twenty Dutch men-of-war, with five thousand troops, were coming to his aid.
The Danish commander, alarmed at this report, hastened to conclude peace with him, on condition that all who had taken part in the rebellion should be pardoned. Christian was to cross to Denmark, and if he could not agree with Frederick was to be free to go to Germany, on giving a solemn oath never again to make any attempt on the three Scandinavian kingdoms.
Before this treaty was confirmed messengers arrived from Frederick who discovered the condition of Christian to be hopeless and insisted on an unconditional surrender. But Knut, the Danish admiral, who had been given full power to act, took Christian on his ships and sailed with him to Denmark, where he insisted that the conditions he had made should be observed.
Frederick and his council were in a strait. To let this tiger loose again was too dangerous, and finally some pretext for breaking the treaty was made and Christian was sentenced to a life imprisonment in the Castle of Sanderberg on the island of Femern. Frederick and his son were obliged to confirm this sentence by a written promise to the Danish nobles that they would never release the detested prisoner.
When Christian learned that the convention had been broken he wept bitterly, lamenting that "he had fallen into the hands of men who cared neither for oaths, promises, nor seals."
These complaints no one heeded. He was taken deep into the dungeons of Sanderberg Castle, and locked up in a dark and narrow prison vault destitute of every convenience, his only companion being a half-witted dwarf who had long been in his service. With the harshness common in those days, and which in his case was well deserved, the door of the cell was walled up, only one small opening being left through which he could receive the scanty allowance of food brought him, and a little barred window through which some sparse light could make its way.
In this dreadful prison the captive remained twelve years without the slightest amelioration of its conditions. Then the door was opened and fresh air and other conveniences were allowed him, but a strict watch was kept up. Finally in 1549, five years later, it being believed that no harm could possibly come from an old man sixty-eight years of age, he was taken to Kallendborg Castle, where he was permitted to entertain himself by hunting or in any other manner he pleased. He lived ten years later, ending in 1559 a life whose misfortunes were a just reward for his faithlessness and cruelty in his day of power.