Ok perhaps I mistyped when I threw in the word “Viking” but it was within a few generation after Rome left when the Saxons quickly moved into Britain setting up the kingdoms of Mercia, Wessex and Kent. Though it was much later when the Danes finally came over and set up Danelaw. But the Vikings had been trickeling into the Shetlands and Orkneys in the mid 8th century.
I will say that I agree that the F-15 was probably the best fighter aircraft in the post-Vietnam era, even to include the A/G F-15E Strike Eagle. The F-16, while a capable airframe, has just had too much mission added to its small frame. Developed under the lightweight fighter program, much of the electronic hardware was not included in the airframe. I believe that is why the Navy chose the F-17 soon to become the F-18 during the F-16/F-17 flyoff. Then the Navy now has their F/A-18E Super Hornet and recently EA-18 Growler to replace the EA-6 Prowler.So then what are your reasons not to include the F-117 or F-14?
There still was the manpower there but not the managerial and logistical system that Rome had to direct it all. Plus once the Romans left, local tribes took over and it would be a long time before any strong leadership would be established in Britain. Hence, Britian's ripeness for the Vikings.
There has to be a balance. We cannot keep this country safe without looking into certain people's behavior. Unfortunately much of those things you say infringe on our freedoms are reactive in nature. No one is watching to prevent crimes/terrorism, most is used to check on who was there and find who comitted the act.You can always move into the woods, grow your own food etc. You still have satillites that can put you on Googlearth.
I would say we most resemble the British Empire. Where as we have created democracy rather than Empiral states subservent to the Empire. As Britain has continued to lose its territories since, well us. The US is loosing its dominance economically. We have assisted many nations to build economic and governmental stability. Initially the US profited from this. Now several of those nations have surpasses us. The teacher is no longer the master. Will we fall? Not in the Roman sense. Perhaps like Britain. We will not be the economic superpower when the rest of the world decides to combine its financial power. It is possible we could remain the backbone of the worlds various military alliances. The core of our Constitution is timeless, Freedom will never fall.
Initially, the generation that watched as the legions left Britain probably had the skills, but as you said, the lack of resources and the missing logistical system of Rome was gone. I believe that the skills were probably lost by the second generation.
While you have a valid point regarding Iron, though bronze was also a simpler metalugistic process, I'm going to say gunpowder. This is where we truely started to look at chemistry and determined that we can unlock energy from within substances. I'm sure someone would be able to provide a roadmap through history from the advent of gunpowder to nuclear warheads. Obviously gunpowder is not that effective unless used inconjunction with iron or steel implements to focus gunpowder's energy. But you can only perfect a sword to a certain point (pun intended).
One thing about much of the people living in the UK is their patriotism to their country, not specifically to the UK. If you talk to anyone over in Scotland, they will tell you they are Scottish before they would say British. Even in England, they are English before British. Basically I think the UK, and even the EU for that sake, are becoming more like the US in the fact that the individual countries have become like our States, part of a single greater government but having some autonomy.
Getting back to the main point of the posts, as for catalysts for war…what about retribution? Didn't Alexander head toward Persia in retribution, and do you think there was a bit of retribution when Hitler moved east? Plus many of the wars between England and France was to take back something taken from them, plus a little extra from time to time.