 Complete the following phrase:  The Cumans first encountered the Rus in 1055, when they advanced towards the Rus Pereyaslavl principality, but Prince Vsevolod reached an agreement with them thus avoiding a military confrontation. In 1061, however, the Cumans, under the chieftain Sokal, invaded and devastated the Pereyaslavl principality; this began a war that would go on for 175 years. In 1068 at the 