Britain and Japan did not have agreements with the United States. I can state that for a fact because I was the United States.
What happened was exactly what happened because the United States did not leave room for England or Japan to attack her.
For instance, there was a 200 point army in North America. No way a landing could be achieved without an awful lot of resources and if achieved, no way a beach head could be established. Thus, neither Japan nor England bothered even trying to form landing parties.
Secondly, Japan was split between attacking Russia and attacking America. Without German assistance, there was no way he could pull off both, not when America was +4 for Canada so at her full 42 IPC for most of the game and pumping out boats like a mad woman.
Eventually, the Japanese navy was sunk and with it, any chance of restraining America. That meant Japan had to go all out against Russia and hope to have enough holdings on the mainland to win without her islands. Meanwhile, America had to go bananas for islands to get enough firepower to make a mainland landing.
Unfortunately, Japan did not have enough left to hold Japan and America squeaked out an invasion, which I may add, was against the odds.
As for England and Russia, I have no idea. I presume from the banter they had a Kill Germany First pact for mutual benefit. As I assume that Germany and Japan had a mutually beneficial pact to kill Russia first. Since they were mutually beneficial, no expressly codified pact was really needed, and I assume never written.
I do think it important to note that, as America, I at no time even posed a threat to Germany. I had no ships in the Atlantic after US 1, nor on the left hand side of the board after US 2. So Germany’s complaints of the entire world against him are really on some shaky footing. Not to mention, after Japan fell, it was America attacking England with a vengeance in Africa and the Middle East. (England was the only threat to me at that time, no one else had a navy and I did not need to worry about land invasions as almost 100% of my holdings were islands and distant continents.) So again, it was not the world against Germany, but rather, Germany and America against England. If anything, the British player should have been complaining about a one sided fight after the fall of Tokyo!