(dramatic music) Britain was on the brink of a much larger and more costly conflict.

One it might not be able to win.

What was going through George's mind?

George III's letters to his prime minister still survive today in the Royal Archives at Windsor Castle.

To help decode them, I've found someone whose time in politics makes her knowledgeable about affairs of state.

Ruth, what are his particular concerns about the campaign and the way it's going?

What's really interesting in this letter, is he works through his thinking.

So, he's saying, at one point, that, "Oh, this only came out from a little tax issue, but now it's grown into the thing that's the most challenging conflict in the world."

He says that really specifically here, "Should America succeed, the West Indies must follow them, Ireland would soon follow the same plan and be a disparate state, and then this island would be reduced to itself."

Basically says, if we lose North America, we lose everything.

The West Indies are going to go, Ireland's going to go, all our merchants are going to live somewhere sunnier, you know, the entirety of Britain will be ruined.

There's going to be... one country falls and then another, and then another, a domino effect right around the British Empire.

Which will leave the, as he calls it, the mother country, as a rump and isolated state.

So, what should George do, then, in this situation, do you think?

I mean, I could imagine that you would send in more and more and more resources, wanting to avoid this domino effect from happening.

Well, we see from the conversations that are recorded in George's voice in these letters that his prime minister is telling him, "Look, we can't actually afford this war.

We would need to send 40,000 new soldiers to kind of put a rebellion down in a land war over there."

And let's remember, in the 1700s, our population was only 8 million people.

This would be a huge army that we would send on top of the troops that are already there.

Is there anything else he could've done instead?

The way usually that you try and avoid conflicts round the world is by signing treaties and doing deals.

But he's got no allies in the world.

France are supporting the colonists.

Spain are also trying to help out.

So, he's isolated, trying to fight a continent away, when he's got a mess at home, he's got almost no money in the public coffers, and he's got no friends in the world.

That explains something I'd always not really understood, which is why he was so intransigent as a war leader.

The thing about George was, he took time to make the decision, but in a sense, the decision almost made itself.

You can read it in his thinking.

There are things that cost more than money to our country.

Even as he's being warned, "Look, we can't afford to have a war in a continent across the sea."

He's like, "Things can cost a nation more than capital.

So what am I going to do?

I'm going to risk it all, I'm going just throw resource at this, and see if we can make it win, and I won't take a backwards step."