"The" Philippines

[Yan Zhang]

Hi,
   I am a Chinese TESOL teacher. In today's dictation exercise, there is a sentence "China is the first leg of the President¡¯s four-nation tour, which also includes Japan, South Korea and the Philippines." One student asked me why there is a "the" in front of Philippines, while usually people don't put definite article before a country name. Could anybody help? Thanks a lot.

Yan