Lithuania was in a good position to conquer the western and the southern parts of former Kievan Rus'. While almost every other state around it had been plundered or defeated by the Mongols, the hordes stopped at the modern borders of Belarus, and the core territory of the Grand Duchy was left mostly untouched. The weak control of the Mongols over the areas they had conquered allowed the expansion of Lithuania to accelerate. Rus' principalities were never incorporated directly into the Golden Horde, maintaining vassal relationships with a fair degree of independence. Lithuania annexed some of these areas as vassals through diplomacy, as they exchanged rule by the Mongols or the Grand Prince of Moscow with rule by the Grand Duchy. An example is Novgorod, which was often in the Lithuanian sphere of influence and became an occasional dependency of the Grand Duchy. Lithuanian control resulted from internal frictions within the city, which attempted to escape submission to Muscovy. Such relationships could be tenuous, however, as changes in a city's internal politics could disrupt Lithuanian control, as happened on a number of occasions with Novgorod and other East-Slavic cities.