What development led to the decline of the Spanish mission system in Georgia in the mid-seventeenth century?

Spanish missions were established for the purpose of religious conversion and instruction in the catholic faith and it saw its decline due to depopulation and forced resettlement of the people.

Explanation:

Spanish mission was established for the sole purpose and intention to convert the people to catholic faith. It had a common place were mass was held and, in that place, the Indian converts were buried. Spanish missions flourished in America as many Indians were attracted to the catholic faith.

As time passed by the American population declined and many forced resettlement of the people happened. Slave raids happened in Georgia also was one factor for the decline of the missions and immigrants joined the pirates' group as slaves and were deported to other countries. Hence there was a huge decline of Spanish missions.