Can someone please explain what drivechain is in simple terms?

I'm also curious about a few things:

What changes need to be made to the protocol to support it? How will it benefit the entire cryptocurrency ecosystem? Why are some people against it? From what I understand, two BIPs are required to fully support drivechain. If successful, drivechain will allow most, if not all, altcoins to become side chains of Bitcoin and inherit its security. Is my understanding correct?

I'm willing to give up to 1000 sats for the best answers!