Final answer:
Nationalism is a political ideology that prioritizes the interests and cultural identity of one's own nation-state over international concerns, which can unite a country or create external conflict.
Step-by-step explanation:
The strong belief that the interests of a particular nation-state are of high importance is best expressed by the term nationalism. This concept refers to a political ideology that values the interests and cultural identity of the nation highly, advocating for national unity and promoting the notion that a nation's interests should be prioritized over international concerns. Nationalism emphasizes the uniqueness and often the perceived inherent superiority of one's own country, and it can lead to a strong desire for self-determination and political autonomy. It has the potential both to unify a country internally and to create external conflicts with other nations. However, this fervent sense of pride and devotion to one's nation can also have a downside, as it may foster hostility toward outsiders and marginalize minority communities within the nation.