When racially charged killings in the 1980s unstitched already flimsy race relations in the city, the Slave Theater grew to be more than just a movie house, it became a symbol and center of black activism.

I found this sentence in New York times. Is the sentence " it became a symbol and center of black activism" a run on sentence or an appositive describing Slave Theater?
Can the appositive have verb "became"

Dependent clause joined by "when" Subordinate conjunction:
When racially charged killings in the 1980s unstitched already flimsy race relations in the city,

Main Clause
the Slave Theater grew to be more than just a movie house

Grammar gurus...any thoughts?