Conrad of Masovia had initiated in 1225 political negotiations with the Teutonic Order of the Holy Virgin, known as the Knights of the Cross. Conrad's error was tragic, his intellectual and political ineptitude obvious. The leaders of the order of the Knights of the Cross invited by Conrad were men of wide political experience, with a broad view of European events. The rulers of Masovia and other duchies, provincial princelings absorbed in their local squabbles, were no match for them.
The order of the Knights of the Cross was founded in 1190 in Palestine, during the Third Crusade and the siege of Accra. Its full name was "The Order of the Teutonic Hospitalier Brothers of the Holy Virgin in Jerusalem." It was founded by the burghers of Bremen and Lubeck for the care of the wounded and the sick, but was transformed only eight years later in a knightly order. It was modelled on the older orders of Joannites and Knights Templar, organized by the knights of western and southern Europe, which achieved great wealth and political power. The members of the Teutonic Knights were distinguished by their white cloaks with a black cross.
The Order stagnated at first and could not summon more than ten knights with their retinues. Its vertiginous career was started by the fourth of its leaders, known as Grand Masters, Herman von Salza, a native of Thuringia. He realized that a German order could not accomplish much in Palestine, which was within the sphere of influence of the Mediterranean nations. It could, however, find more rewarding opportunities in regions closer to Germany.
In 1211 the Knights of the Cross secured from Andrew II, king of Hungary, a grant of land and a charter in Transylvania. They were supposed to fight there against the tribes of the steppes, but instead set out immediately to establish their own state. Andrew II had participated in the crusades, knew Palestine and learned there a good deal by observing the tactics of other military orders, weakening and disrupting the kingdom of Jerusalem. After his return he soon grew wise to the designs of the Knights and expelled them from his country in 1225, disregarding the pope's protests.
Unfortunately Conrad of Masovia, who was starting his relations with the Knights of the Cross at the time, was not as well informed and acted without understanding the situation. His opposite number was a politician of remarkable skill, Herman von Salza himself.
The emperor was at the time Frederick II of the House of Hohenstauf, a brilliant monarch, almost modern in his outlook. He was virtually a foreigner to the Germans, as the center of his power was in Sicily and Naples. Herman von Salza was his confidant and close advisor. The Grand Master of the order had sworn allegiance to both the emperor and the pope.
Under Frederick II, the Knights of the Cross played a key role in European politics. One of them was the administrator of Alsatia on the Rhine, other held important positions in Palestine. It was said that all of Germany was governed through their influence and it was not surprising that the emperor chose them as the agents of his policy on the shores of the Baltic. The empire was about to reach the end of its greatness -- soon after the reign of Frederick II it went into decline and lost its dominant position for a long time. The Knights of the Cross were its political heirs in the east but Conrad of Masovia had no idea with whom he was dealing.
In 1224, the emperor issued a charter concerning the Baltic countries, including Prussia. He promised protection to the people of these lands, providing they converted to Christianity, and equal rights with his other subjects. At the same time he set them free of any allegiance to other prince and kings. The document amounted to a declaration of the emperor's sovereignty over the Baltic countries.
In 1225 Conrad of Masovia proposed to the knights that they should help him in the defence against the Prussians, in exchange for the grant of the region of Chelmno. Actually he planned to have them conquer Prussia for him.
In 1226 Herman von Salza received from the emperor a charter which provided the legal base for his activity in Prussia. Frederick gave the knights the region of Chelmno (which he had no right to do, as Poland was not subject at the time to the suzerainty of the empire). He authorized them to invade and occupy Prussia and also endorsed their state laws, applicable to the pagans as well as to Christians.