One question raised in my mind, why lord Vishnu incarnates only in Bhartha Varsha (India)? It is little bit confusing for me, because I can't find any valid resources. Please provide some evidence through the scriptures.
If we just talk about known oldest Civilization, Indus civilization(mohenjo daro or harappa civilization) comes into our mind.
If you List the Oldest civilizations, you will not find more that 10-12, That means that other world was not developed/grown enough or people didn't live there at that time.
Referencing from the above point we can conclude, As Indian scripture says, We are living in KALYUGA which is 5000 year old, That time no other place was developed enough.
This way you might link the logic (connect the dots)..