The Federation has long prided itself that it is an organisation dedicated to peaceful coexistence; indeed, it is the only known power in the alpha quadrant which has no dedicated military arm whatsoever. Instead it relies on Starfleet, a body whos primary role is exploration and scientific research, to fulfil the defence role also.
Nevertheless, the last decade has seen the Federation faced with an alarming number of clear and serious threats to its security; the more aggressive stance taken by the Romulans after so many years of inactivity was followed quickly by first contact with the Borg and then the Dominion. The recent rift between the Federation and the Klingon Empire saw that powerul ally an enemy and the Federation without allies for the first time in decades.
It is little wonder then that Starfleet has been burdened with an ever-increasing military role; ships designed primarily for peace have had to participate in conflict after conflict. Many pundits predicted that Starfleet and the Federation itself would be too weak to survive such a situation. The last decade has demonstrated just how wrong they where.