National days are the days which are very special and important for a nation.A National Day is a special day where people celebrate their country or nation each year. Most countries have national days and they are usually a national holiday, where people don't go to work or school. In many countries which used to be colonies, the national day is known as because it remembers the day they became free of their old empire. In other countries like China, the national day remembers when the old government of the country changed to the new one. In the past, the king or emperor's birthdays were often treated as a kind of national day.