State of Decay 2 - Time is your worst enemy

So about those missions…I was just visiting a new enclave (The Doctors, sadly they had zero sonic screwdrivers for trade) and while I was there they got attacked by “Raiders”. I helped them to successfully kill all 4 people who attacked the enclave (and got some nice loot from the bodies). Now though I am wondering, did I just kill off another enclave somewhere or do raiders just magically appear from nowhere to threaten your home base and other enclaves?

Also, working vehicles seem to be in much shorter supply in SoD 2. I’ve been playing for hours and explored pretty much all of the camp town where you start and driven all over the larger town where the truck stop is and have yet to find another driveable vehicle aside from the SUV I brought with me from the prologue. Does that magically fix itself when I finally get around to taking over the truck stop and officially ending the tutorial phase?