Briefly it's this way.

A few weeks ago, while the Allies thought they were fighting the Boxers, it came to the knowledge of my brother, the Foreign Secretary, that the Tsung-li-Yamen had concluded a secret treaty with Russia which practically annulled all our rights over the Yang-tse Valley, and gave Russia the right to bring her Northern Railway right down through China.
"As you know, we've stood a lot too much in that part of the world already, but we couldn't stand this; so about ten days ago an ultimatum was sent declaring that the British Government would consider any encroachment on the Yang-tse Valley as an unfriendly act.
"Meanwhile France chipped in with a notification that she was going to occupy Morocco as a compensation for Fashoda, and added a few nasty things about Egypt and other places.

Of course we couldn't stand that either, so there was another ultimatum, and the upshot of it all was that I got a wire late last night from my brother telling me that war would almost certainly be declared to-day, and asking me for the use of this craft of mine as a sort of dispatch-boat if she was ready.

She is intended for something very much better than fighting purposes, so he couldn't ask me to use her as a war-ship; besides, I am under a solemn obligation to her inventor--her creator, in fact, for I've only built her--to blow her to pieces rather than allow her to be used as a fighting machine except, of course, in sheer personal self-defence.
"There is the telegram from my brother, so you can see there's no mistake, and just after it came a messenger asking me, if the machine was a success, to bring this with me across the Atlantic as fast as I could come.

It is the duplicate of an offensive and defensive alliance between Great Britain and the United States, of which the details had been arranged just as this complication arose.