In 1240, Batu Khan sacked Kiev, Volyn and Galich. In those years, there were feuds in these cities. Knyaz Roman, who united Volyn and Galich and died in 1205, had two children: Daniil and Vasilko. Only after a twenty-five years long struggle with neighbor knyazes and boyars, Daniil became a knyaz of Galich and Kiev. (He even had to escape with his mother, nanny and a monk to Poland and then to Hungary. They got assistance there and managed to return to Rus. For many years, Volyn and Galich were contested by Russian knyazes, Poles and Hungarians.)
As soon as Daniil finally broke the resistance of the boyars, Batu Khan came to his lands and Daniil had to flee again to Poland. He returned only the Mongols left. To restore the sacked cities, he invited the settlers from other countries: Poland, Germany, Hungary. Accepting the dominance of the Mongols, he took steps to the liberation from their power. He established relations with the West, sent emissaries to the Pope, promising him to unite the Orthodox and the Catholic churches, and planned a crusade against the Mongols. The Pope sent him a king's crown and in 1255 Daniil was crowned as a king in Drogichin. However, the crusade failed and Daniil got almost no assistance from the West. Daniil broke the relations with the Pope and found another ally — the Lithuanian prince Mindaugas. At this time, the Mongols began to suspect that he is plotting against them and sent an army demanding to destroy his new fortresses. Not daring to oppose the enemy, Daniil agreed.
Daniil often interfered the affairs in Hungary, Czechia, Austria and Poland, he had relatives in many European countries, encouraged trade with the West and welcomed foreigners in his lands. These relations were a logical corollary of the geographic location of his country, on the edge of Rus, near with Poland and Hungary. These relations became a reason of the loss of independence of Galich and Volyn after Daniil's death.
Like other western Russian regions, the duchy of Daniil was often attacked by Lithuanians. Daniil was in the permanent conflict with Mindaugas and the Lithuanian tribe of Yatvyags. While the weak knyazes in the North gave up, Daniil attacked himself and overran his enemy. Finally, Yatvyags had to pay tribute to the knyaz of Galich. Mindaugas offered Daniil to marry their children. Daniil's son, Shvarn, married Mindaugas' daughter and Daniil got strong influence in the duchy of Lithuania. This influence grew even larger after the death of Mindaugas, when the army of Shvarn established order in Lithuania and assisted Mindaugas' son, Voishelk.
In 1264, Daniil died. By this time, the feuds in the south-western Rus were stopped, the power of the knyaz strengthened, the wealth of the duchy grew. Rus became influential in the affairs in the Middle Europe, Lithuania was pacified. The dominance of the Mongols was weaker here, probably, because this duchy was the most distant from the Mongolian lands. However, the heirs of Daniil were incapable of keeping this prosperity. The knyazes of Galich and Volyn after Daniil, his sons, nephews and grandsons were constantly fighting with each other, boyars restored their privileges, citizens, many of whom were foreigners, demonstrated no patriotism. Foreign countries began to interfere the affairs of south-western Rus. Lithuania became so strong by the XIV century that attempted to conquer the south-western Rus. The Lithuanian princes succeded in capturing Volyn in mid-XIV century. At the same time, Poland seized Galich. So, the heritage of Daniil of Galich was lost.