To differentiate ethnicity and nationality mostly depend on one’s ideology, this concept has brought people together and also can tear people apart due to their differences. Nationality can be defined as members of a particular state or nation by birth, origin, ownership; nationality can also be referred to as citizenship.
It indicates the country a person belongs to. Nationality also arises mainly from your geographical location.
Ethnicity can be defined as a personal identity based on their culture, examples of characteristics that indicate a person's ethnicity is their language, food, mode of dressing, religion, and many more.
Your ethnic group differentiates you from others even though you claim the same nationality.