In Cisco Student Guide, it says that the Router BGP command does not activate BGP. However, on my lab router, it shows this:
(config)#router bgp 5500
(config)#router bgp 5600
BGP is already running; AS is 5500
you cannot have a router on both BGP AS 5500 and BGP AS 5600 I usually use this to show this.
A BGP AS is owned by a company that got it from RIPE or ARIN (Regional Internet Registries)
And I agree with you once you enter router bgp 5500 the process is created.
Very good point
Hope to help