Entry into a country — crossing a national border to enter a state; usually involves immigration control and visas.
日本に入国する際はパスポートと入国カードが必要だ。
When entering Japan you need a passport and an immigration card.
入国審査で質問に答えるのに緊張した。
I was nervous answering questions at immigration control.
祝日のため入国者が増え、空港は混雑していた。
Because of the holiday, arrivals increased and the airport was crowded.