A passport is always required when traveling from one country to another. This is the authorized identification document issued by your country of citizenship that confirms your identity and nationality.
What is passport?
Passport is a legal certificate issued by one's mother country to testify its owner's nationality and identity when crossing one country's frontier into another for travel, work and residence overseas. Actually the word "passport" in English means the pass of a port. In other words, the passport is the proof for a citizen to go through the international ports of all countries. Some countries may issue a kind of general credentials to replace the passport.
For international travel across borders, a citizen must possess a legitimate passport which issued by his own country's government, and simultaneously, an effective visa to your destination country is also often required.
If you should have an accident during the period of travel or residence abroad, the host country should first confirm your status and nationality according to your passport, and then decide what to do next and how to handle it well. Similarly, the country which issued the passport and its embassy or consulate stationed abroad also has to decide how to offer help or diplomatic protection based on this passport.