What is the main purpose of building an airport by reclamation in the South China Sea?

Expand jurisdiction and improve defense capabilities. According to the query law, we know that:

1. Expanding jurisdiction: It shows that China has indisputable sovereignty over Nansha Islands and its adjacent waters. The main purpose of building an airport by reclamation in the South China Sea is to expand jurisdiction.

2. Improving defense capability: The main purpose of providing a strategic base for China's naval modernization is to improve defense capability and safeguard national sovereignty and territorial integrity.