Question

why USA is called the USA and why india is not called the India

Answer 1

'The' is never used before any proper nouns. 'India' and 'America' are the proper nouns. In 'The United States Of America', 'the' is used before the adjective 'united'.

Answer 2

We use 'the' in front of United States of America because United is a common noun. So we use 'the' in front of countries if the name contains a common noun. But India has its own name and does not share its name with any other country, so we do not use 'the' in front of India.