Simplify the following text for a Grade 4 native English-speaking person.
Original: Southeast Asia is geographically divided into two subregions , namely Mainland Southeast Asia ( or Indochina ) and Maritime Southeast Asia ( or the similarly defined Malay Archipelago ) ( Indonesian : Nusantara ) . The Andaman and Nicobar Islands of India are geographically considered part of Southeast Asia .
Simplified: These are the countries in Southeast Asia :