Which of the following territories had missions established by junipero Serra that housed more than 18,000 Native American converts?

Answer: California

Explanation:

Junipero Serra was an important Franciscan friar that started the settlement of California by constructing a Catholic mission at San Diego. Following him, for the next 50 years, another 20 more Franciscan missions established the foundation of California. In those more settled regions, the original missions were converted into secular parishes, and the property was divided among the Indians. In California, the missions were much larger, more influential, and longer lasting. The Franciscans used overwhelming force to control the Indians as captive laborers in the missions. Rebellious Indians were whipped or imprisoned. Mission Indians died at an alarming rate, mostly by infectious disease, in second came the exhausting labor as well. The Native American population along the California coast declined from 72,000 in 1769 to 18,000 by 1821.

California, my friend!