Nationalism and archaeology are two different things, but they are connected. Nationalism is feeling proud and strong about your own country and culture, including the history and heritage of the place from the past. Archaeology is the scientific study of past cultures by studying artifacts such as tools and pottery, ruins, and the way people lived.
Archaeologists look at ancient things, like what people used to eat, or the clothes they used to wear hundreds or thousands of years ago, to learn about the history of a place. Nationalism often takes these findings and uses them to celebrate the shared history of a group of people, like a nation or culture, to make people feel proud of their heritage. In a way, archaeology can be used to help people feel more connected to each other, and to their past.