The NCR-Enclave War was a military conflict between the New California Republic, the Brotherhood of Steel and the Enclave, that began at some point after the Oil Rig's destruction and ended sometime after with the destruction of Navarro. Precisely when this occurred is unknown.
Several years after the Chosen One would destroy the Oil Rig, the NCR would decide that Navarro and the rest of the Enclave would be a threat to the security of the region and attacked. The NCR would sack Navarro and destroy the Enclave presence in the Core Region. From there on, the NCR, while bilateral relations with the Brotherhood were still good, would hunt down the surviving Enclave forces. While many Enclave would go into hiding, the Brotherhood would assist the NCR in arresting them for war crimes and thus relatively few managed to live in NCR territory by hiding their identity.
While most of the pockets of remnants located in California were arrested, many moved to Nevada. There were often stories of remnants being arrested for war crimes from time to time or having managed to live in the NCR territory by hiding their identity, though this would be usually used to scare children.
The use of Enclave equipment in Navarro by the NCR would inadvertently bring about the destruction of the Divide.