How can this sense of nationalism be a bad thing in society?

A sense of nationalism that is too large can affect one country's relations with another country. These bitter relations were the primary cause of WW1.

Explanation:

map scale refers to the relationship (or ratio) between distance on a map and the corresponding distance on the ground. for example, on a 1: 100000 scale map, 1cm on the map equals 1km on the ground.