At one time Mission San Carlos Borromeo, just outside Monterey California, was the capitol of the Spanish Empire in Alta California. Junipero’ Serra, the founder of the California mission system, and now a Saint, is buried in the chapel. Jose Antonio Romeu, the second Spanish Governor of all California is buried there too. Today it is beautiful and celebrated, but by 1863, the place was in ruins.
The short answer is the end of slavery in Mexico.
When the missions were first established they technically “belonged” to the local inhabitants aka Indians. It was their land and their buildings, but the management was sort of leased to the Catholic priests for a period of time to help get things up and running. At least that is how it was drawn up on paper.
In reality, the way it worked out, was that the Spanish forced the local native inhabitants to build, and then work in, these palatial compounds.
They were indeed palatial.
When the lease on Mission Carmelo ran out, the Franciscans in charge simply kept control. There were no non-European authorities nearby to force them otherwise, and the native locals were already effectively slaves.
So the place stayed splendid.
Then, in 1821, Mexico won its own American revolution and kicked the Spaniards out. Soon after the new government issued a proclamation of emancipation (42 years before Lincoln), freeing the enslaved Indians, who then left the missions.
Without an unpaid workforce the missions couldn’t support themselves and they began to decline.
Then the Mexican government went a step further and confiscated the missions from the Catholic church and started selling off the surrounding lands and most of the fancy stuff inside got ransacked- or carried off by retreating friars.
As a side note, this same crack down on Mexican slavery caused a dust up in what became Texas, since the white Americans who recently moved there still wanted the right to keep other people as slaves.
But eventually California became America, Catholics, Indians, Mexicans, and all- and in 1931 real work got underway in restoring Mission San Carlos Borromeo de Carmelo, or just the Carmelo Mission as most people know it, to its original glory.
They didn’t exactly tell that story when I visited. The pamphlets have bits and pieces, and the tour guides are happy to tell you about some artifacts, but mostly its just a church that hosts touring 4th graders.