Wikipedia
The Koliyas were Kshatriya of the Adicca ( Iksvaku) clan of the Solar Dynasty during the time of Gautama Buddha. The family members of these two royal families married only among themselves. Both clans were very proud of the purity of their royal blood and had practised this tradition of inter-marriage since ancient times. For example, Suddhodana's paternal aunt was married to the Koliyan ruler Añjana. Their daughters, Mahamaya and Mahapajapati Gotami, were married to Śuddhodana, the chief of the Sakyans. Similarly, Yashodhara, daughter of Suppabuddha, who was Añjana’s son, was married to the Sakyan prince, Gautama Buddha. Thus, the two royal families were related by marriage bonds between maternal and paternal cousins since ancient times. In spite of such close blood-ties, there would be occasional rifts between the two royal families, which sometimes turned into open hostility.