How did changes in the balance of land versus naval balance of power prevent England from being successfully invaded by foreign powers after 1066?

Question

The last successful invasion of England was that by the Normans in 1066. Prior to that, England had been successfully invaded by waves of Angles, Saxons, and Jutes from the Continent, and before that, the Romans.

After 1066, no one from the Continent successfully invaded England. These include Hitler, Napoleon, the Spanish Armada, and possibly the French during the 100 years war. "Native" invaders like William and Mary, (the latter of whom was English) or Henry Beaufort or the Barons in the First Barons War did sometimes succeed.

The key factor appears to be that in the second millennium, England had a "critical mass" of naval clout to defeat the various would-be foreign invaders, but this was not true in the first millennium. If so, what would be the key ingredients of this naval "critical mass?" What caused this change? Was it due, for instance, to the greater efficacy of ships built in the second millennium in patrolling the waters around England?

Or put another way, why were first millennia foreigners more successful in invading England, given the same weather, and more primitive ships (unless the argument might be that the weather changed and we had e.g., a new ice age in the second millennia and not the first).

Answer 1

There are plenty of opportunities to argue against the premise of the question here. The exception made for native invaders in particular is not particularly convincing. The "Glorious Revolution" could certainly be counted as a Dutch invasion. Henry Tudor's invasion had signficant Breton support. The Spanish Armada could easily have gone another way, had the weather been more favourable on them.

However, once we get to Napoleon something clearly has changed about the "invadability" of Great Britain. Here we have a brilliant military leader with a significant army on the French coast and more than enough motivation to invade Great Britain - but he doesn't try.

The crucial change between William the Conqueror and Napoleon is how naval combat works. The traditional form of naval combat is that you tie together the ships, and then fight hand-to-hand. A warship will be more in control over whether or not to fight than a troop transport, but will not necessarily have a significant advantage if the fighting happens. However, once cannons become the standard, utterly wrecking the enemies troop transports with your warships becomes an option.

Accompanying the technological development is that a supporting a substantial navy is a significant challenge for a state, and only in the early modern period did European states again reach the required level of centralisation and government budgets.