(The N is pronounced like 'n' in 'gun'. The DH is pronounced like a hardened sound of 'th' in 'brother'.)
Gaandhaara was the name of one of the western-most provinces of ancient India. .This roughly corresponds to present Kaandahaar. During one of the Mughal rogues, we lost it to Kaabool.
As was the custom in Samskritham, contry names are given by the people that inhabitted it and the name is always in plural.
The king of a country derives his name by the country he ruled. E.g. Paanchaala is the ruler of the country Panchaalam,
Chaidya is the ruler of the country Chedi, Maagadha was the ruler of the country Magadha etc. King of Gaandhaara provonces is described as Gaandhaara, the difference being only in the ending that is specific to Samskritham language. Gaandhaaraas implies the province and its people too.
During the Mahaabhaaratham period, Gaandhaara was ruled by Shakuni who was maternal uncle of the Kouravas. ( his sister Gaandhaari was Kouravas' mother.).Naturally he was a strong opposer of Paandavas.
One of shakuni's sons fought against Arjuna during the latter's Ashvamedham expedition, after the war. But, in the end, he lost and surrendered to Arjuna.
"After praying to Naaraayana, Nara, Sarasvathi and Vyaasa, then one should read the Jayam."
DEDICATED TO MY DEAR NIECE VYSHNAVI KRISHNA