The United States of America why not "The India"

I know that this question is faced by all of us. And, we are not satisfied by any conclusion. Last time when I was watching the movie "English Vinglish" the actress Shri Devi asks a question to her English teacher Why "The United States of America" why not "The India", but the Teacher has not

answered to her question and we (I) thought that there are some uncertain rules which were created

by English people. So they use English as they want and the word "The" is used before United States of America for showing its importance in world.



Is my (or Our) thinking is right about the above mentioned matter? Now you will search the answer where you can find it. And, I did the same thing. Today, I was searching some English Grammar  related sites and have read a page where the details about the English articles were mentioned you can click here and find it. Still you can read below details about where the article "The" is not used:

Rule:

Article “the” is not used for names of countries of places. e.g. New York, America, Mexico, Japan, London. But article “the” is used for a name, if it expresses a group of place, states, or land. e.g. The United States, The Philippines, The Netherlands